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ELECTRICIANS' 

OPERATING AND 
TESTING MANUAL 



A HAND BOOK FOR MEN IN CHARGE OF ELEC- 
TRICAL APPARATUS, REPAIR MEN, TROUBLE 
MEN, LAMP TRIMMERS AND ELECTRI- 
CIANS GENERALLY 



BY 



HENRY C. HORSTMANN 

AND 

VICTOR H. TOUSLEY 

AUTHORS OF MODERN \YIRING DIAGRAMS AND DESCRIPTIONS: 

MODERN ELECTRICAL CONSTRUCTION; ELECTRICAL 

WIRING AND CONSTRUCTION TABLES: PRACTICAL 

ARMATURE AND MAGNET WINDING: ETC. 



ILLUSTRATED 



CHICAGO 
FREDERICK J. DRAKE & CO. 

PUBLISHERS 






Copyright 1916 

BY 

HENRY C. HORSTIVIANN 

AND 

VICTOR H. TOUSLEY 



Copyright 1910 

BY 

HENRY C. HORSTMANN 

AND 

VICTOR H. TOUSLEY 



C 



\ 



24 1916 '^ 



MAR 24 1916 



C1,A428258 



i PEEFACE 

The object of this work is to instruct the practical 

.electrician in the management, operation and testing 

^. of the more important electrical devices now in use. 

^ Almost every line of industry, great or small, now 

has much to do with electric motors and lights, to say 

nothing of the ever increasing number of small isolated 

plants using gas or gasoline engines in connection with 

electrical generators. 

From observation of many such plants in actual 
operation it has long been apparent to the authors 
that some hand book giving in a condensed, simple 
manner all of the instructions needed for the intelli- 
gent installation and operation of electrical devices is 
greatly needed. 

The method adopted has been that of familiarizing 
the student w^ith the underlying principles governing 
the design of motors, dynamos, arc lamps, etc., rather 
than to go overmuch into detail on the construction 
of particular commercial forms. It is confidently be- 
lieved that the student who has mastered the general 
theory of dynamos, motors, etc., will have no difficulty 
in comprehending such variations in their application 
as he may meet with. 

In order to avoid unnecess-ary bulkiness and to give 
the reader as much of the necessary information as 

3 



4 Preface 

possible within the limits of the space, all catalogue 
cuts have been omitted; it being assumed that the 
reader is familiar with the general appearance of 
motors, arc lamps, storage battery, etc. 

It is in the hope that this work may meet with the 
same success and kindly reception as previous efforts 
of the authors that this volume is offered to the public. 

THE AUTHORS. 



TABLE OF CONTENTS 

CHAPTER I. Page 
The Electric Current 7 

CHAPTER II. 
Electrical Units 14 

CHAPTER III. 
Magnetism 19 

CHAPTER IV. 
Principles of Dynamo Electric Machines 39 

CHAPTER y. 
Types of Dynamos 56 

CHAPTER VI. 
Principles of Electric Motors — Direct Current 74 

CHAPTER VII. 
Types of Motors — Direct Current 80 

CHAPTER VIII. 
Principles of Alternating Current Motors S6 

CHAPTER IX. 
Types of Motors — Alternating Current 96 

CHAPTER X. 
Dynamo Operation — Direct Current 102 

CHAPTER XI. 
Operation of Alternators 124 

CHAPTER XII. 
Motor Operation 145 

V 



vi Tahle of Contents 

CHAPTEE XIII. 
Transformers 151 

CHAPTEE XIV. 
Batteries 170 

CHAPTEE XV. 
Arc Lamps 184 

CHAPTEE XVI. 
Incandescent Lamps 217 

CHAPTEE XVII. 
Nernst and Cooper Hewitt Lamps 239 

CHAPTEE XVIII. 
Instruments for Testing 243 

CHAPTEE XIX. 
Testing 269 

CHAPTEE XX. 
Dynamo and Motor Troubles 298 

CHAPTEE XXI. 
Eecording Wattmeters 307 

CHAPTEE XXII. 
Life and Fire Hazard 342 

CHAPTEE XXIII. 
Ground Detectors and Lightning Arresters d47 



iuf 



CHAPTEE I 

THE ELECTRIC CURRENT 

By the electric current is meant that agenc}" which 
comes into action when a circuit containing an elec- 
tro-motive force is closed. Electro-motive force is, as 
the name implies, the impelling force, and the circuit 
is the system of conductors along which alone elec- 
trical action takes place. This flow of current is quite 
analogous to the flow of water in a system of piping 
or over the surface of the earth. Such a flow of water 
can take place only when the water is at different lev- 
els, or, when from any cause, a difference of pressure 
exists between different points. When either or both 
of these conditions exist the flow always takes place in 
a certain direction, i. e., from the high level or pressure 
to the lower, and this flow is always more or less dimin- 
ished by obstacles or resistances. The same observa- 
tions hold true of electric currents ; they flow only in 
obedience to electrical pressure; they flow always in 
a certain direction determined by that pressure and 
the quantity of the flow depends, or is governed, other 
things being equal, by obstacles w^hich are spoken of 
as resistances. 

"We cannot prove, and it is not necessary, that there 
is any actual direction, or, much less, a change of direc- 

7 



8 Operating and Testing 

tion, or even a flow of current, but the phenomena no- 
ticed make the assumption a very convenient one and 
it is, to say the least, very helpful in the study and 
application of these phenomena. 

Eefer now to Figure 1 which shows a common glass 
jar nearly filled with water and which also contains 
a small quantity of sulphuric acid and one plate of 
zinc Z and another of copper C. While the two ends 
of the wires connected to the plates remain apart 
there is no flow of current, but an electrical pressure 



Figure 1 

exists, as can readily be shoA\Ti. As soon, however, as 
we bring the two ends of w4re together a flow of cur- 
rent takes place. It is the high resistance of the air 
between the two terminals of the wires which prevents 
the flow of current in this case, just as the resistance 
of the valve in a water pipe prevents the flow of 
water when it is closed. 

The direction of the flow of current is said to be 
from the zinc to the copper inside of the cell and from 
the copper back to the zinc in the exterior circuit or 



The Electric Current 



9 



outside of the cell. In all batteries (a battery is a 
number of cells coupled together) the copper plate or 
terminal is spoken of as the positive or -f- pole from 
which the current flows and the zinc plate as the neg- 
ative or — pole toward which the current flows. From 
the cell shown, which is the simplest of all forms, we 




Figure 2 



can obtain but a very insignificant current, and that 
for only a very short time, for reasons to be given 
later on. If we couple a number of cells together, as 
conventionally indicated at 'B in Figure 2, we shall be 
able to obtain a considerable current. In this repre- 
sentation of a battery the long thin lines stand for 
the copper plate from which the current flows to the 



10 Operating and Testing 

outside circuit and the short thick lines stand for the 
zinc element from which the current flows inside of 
the cell to the copper element. 

Figure 2 has been drawTi principally to acquaint 
the reader with the general effects obtainable from the 
electric current. In the outer system of wires W, W, 
etc., the same current passes through all of the de- 
vices, and this is known as a series circuit. R repre- 
sents fine wire, which will be heated to redness or 
even melted if the current is made strong enough. At 
A is showTL the manner in which an arc or a flash 
may be produced; first bring the ends of carbon or 
metal together until the current is started, then sep- 
arate them a little and the current will continue, thus 
forming a very hot flame known as the electric arc. 

If a wire carrying a current be wound about an 
iron core M, magnetism will be generated and enable 
the iron bar to attract other pieces of iron. This 
magnetism will exist only while the current is flowing. 

If the current is forced to pass through water, as 
indicated at E, it will decompose it and this decompo- 
sition will be noticeable by the bubbles of gas given 
off. If the current pass through a suitably prepared 
bath in which metals are properly connected to the 
wires, the metal will be eaten away from the positive 
pole and deposited at the negative. 

The arrangement of wires shown at I, I^ is drawn to 
illustrate the method of inducing currents of electric- 
ity in transformers. "When a current is passed around 
the bar at I a current will be induced in I'. This 
current will last only a very short time, but if I is 
connected to a circuit in which the current is contin- 



The Electric Current 11 

ually changing in value the induction of currents will 
follow every change in current strength and it is pos- 
sible to arrange these variations in such a manner that 
light may be obtained from these induced currents. 

The inner circuit shown connected to the battery by 
heavy lines is known as a parallel circuit, all oi the 
devices being connected in parallel instead of in series 
as in the other. In such a circuit each device is inde- 
pendent of the others and the current increases in 
proportion to the need^ of the devices connected. The 
more there are connected the greater becomes the cur- 
rent, but the voltage need not be increased. In a se- 
ries circuit the more devices there are connected the 
more cells of battery must be provided to increase the 
pressure so that the current may remain the same. 
Only such devices as use the same amount of current 
can be run in a series circuit. 

In the parallel circuit at C there is shown a con- 
denser. A condenser is an arrangement of plates 
which is capable of taking a charge of electricity at 
rest much as a jar is capable of taking a charge of 
water. The positive and negative plates of a con- 
denser are perfectly insulated from each other and a 
current of electricity cannot pass from one to the 
other. When, however, the plates are connected to a 
source of current a small quantity of current will pass 
into the condenser. Such a charge may be held in a 
condenser for some time or will pass out of it when 
the voltage at the terminals is withdrawn or the circuit 
around the condenser closed. Enough current can be 
made to pass in and out of a small condenser to affect 
a telephone receiver T, or a sensitive polarized bell. 



12 Operating and Testing 

CONDUCTORS AND INSULATORS 

An appreciable current flow can take place only in 
a system of electrical eonductors. The best conductors 
are the various metals in the order here given : silver, 
copper, gold, platinum, tin, lead, etc. The difference 
in favor of silver as against copper is so small com- 
pared to the higher price of silver that the latter is 
seldom used. A pound of copper will, under the same 
circumstances, carry about 6 or 7 times as much cur- 
rent as a pound of iron and as this fact makes copper 
much cheaper than iron, copper is the metal almost 
universally used for electrical purposes. 

It is not, however, sufficient to provide conductors 
along which the current can flow; it is also necessary 
to surround these conductors with some material which 
will prevent the current from flowing anywhere ex- 
cept along these conductors. A bare copper wire lying 
on some other conducting material can no more be 
depended upon to carry the current than a lot of 
broken or disconnected pipes can be depended upon 
to carry a stream of water. Even under such condi- 
tions the current may flow along the \^dres and the 
water may flow along the pipes if these happen to 
offer the easiest path, but in neither case will it be 
possible to get any work done. To get the proper 
service from either we must be able to force the flow 
where our machinery needs it ; whatever portion of it 
we can not so confine is a direct loss. 

Such materials as resist the flow of current suffi- 
ciently to prevent its escape from the conductors in 
appreciable quantities are kno\Mi as insulators. Some 



The Electric Current 13 

of them are: air, glass, silk, rubber, dry asbestos, 
porcelain, slate, marble, wood, mica, shellac, paraffine, 
etc. All insulators to give the best service require to 
be dry. If they are wet current will leak through the 
body of those that are porous and over the surface 
of those that are not. It should be borne in mind that 
there is no such thing as, either a perfect conductor 
or a perfect insulator. Every conductor offers some 
resistance to the flow of current and no matter what 
the insulator may consist of, if we but make the pres- 
sure great enough we can force some current 
through it. 



CHAPTER II 

ELECTRICAL UNITS 

In order to make any practical use of electricity we 
must be able to measure it, and for the purpose of 
measurement and calculation the following units have 
been adopted by electricians, and in turn legalized by 
the U. S. government: 

The ohm as the unit of resistance. 

The ampere as the unit of current flow or current 
strength. 

The volt as the unit of eleetro-motive-force or elec- 
trical pressure. 

The coulomb as the unit of quantity. 

The farad as the unit of capacity. 

The joule as the unit of work. 

The watt as the unit of power. 

The henry as the unit of induction. 

THE OHM 

The ohm is the unit of resistance. Resistance is a 
property possessed by all materials, but in varying de- 
grees. It always varies inversely as the cross-section 
of the material ; that is, the larger the wire the less 
will be its resistance and the smaller the wire the 

14 



Electrical Units 15 

greater will be its resistance. The resistance of all 
materials increases directly as the length, and is, also, 
to a small extent, affected by a rise in temperature. 
This resistance acts electrically much as friction does 
mechanically; it is very useful in the proper place 
and very objectionable in the wrong place. It is this 
resistance in the filament of a lamp that gives us light 
when current is forced through it, and heat in the 
heater, but it is also this resistance which causes the 
loss in voltage or pressure which makes it so difficult 
to transmit currents of magnitude over wide areas. 
Resistance tends to diminish current flow and, when 
great enough, prevents it entirely. 

The legal ohm is equivalent to the resistance of a 
column of mercury 106.3 centimeters long, 14.4521 
grammes in mass and at the temperature of melting 
ice. As an illustration of more practical value : 2 3/10 
feet of No. 36 B. & S. gauge wire has a resistance of 
one ohm ; 380 feet of No. 14 wire a resistance of one 
ohm and 1,000 feet of No. 10 wire a resistance of one 
ohm. 

THE AMPERE 

The ampere is the unit of current strength. It ex- 
presses the rate of current flow. It is not correct to 
speak of it as measuring quantity. To obtain the 
quantity we must multiply the amperes flowing by the. 
length of time they flow. The heating of a wire, the 
chemical action and the magnetism produced are all 
due to the amperes flowing in the circuit. The legal 
ampere is that current, which, when passed through 
a solution of nitrate of silver, prepared in accordance 



16 Operating and Testing 

with certain specifications, deposits silver at the rate 
of 0.001118 grammes per second. 

It is the current which results from a pressure? of 
one volt acting in a closed circuit on a resistance oJ 
one ohm. A 16 c. p. 110 volt incandescent lamp re- 
quires a current of one-half ampere; an open, series 
arc lamp a current of about 10 amperes. 

THE VOLT 

The volt is the unit of electro-motive-force, or elec- 
trical pressure. It is this pressure which is the imme- 
diate cause of current flow and we speak of it as of so 
many volts, just as we speak of steam pressure as of 
so many pounds. 

The volt is defined as the electro-motive-force which 
will force a current of one ampere through a resist- 
ance of one ohm. This is equal to about 1000/1434 
of the electro-motive-force of a Clarkes cell. The com- 
mon wet carbon battery gives about 1.2 volts; a stor- 
age battery about 2 volts per cell. 

THE COULOMB 

The coulomb is the unit of quantity. It is the cur- 
rent delivered by one ampere in a second. To find the 
number of coulombs we multiply the number of am- 
peres by the time in seconds. This unit' is seldom used. 

THE FARAD 

The farad is the unit of capacity. Under certain 
circumstances electrical conductors and certain ap- 
pliances chiefly known as condensers can be heavily 
charged with static electricity (electricity in a state 
of rest) and can be again discharged; and, in fact, if 



Electrical Units 17 

subjected to an alternating electromotive-force this 
charging and discharging is continually taking place. 
This charge depends upon the nature of the material 
out of which the condenser is made upon the number 
and size of the plates and upon the electro-motive-force 
of the circuit. The more current there is forced into 
a given condenser the greater will be its potential dif- 
ference. This can not, of course, be greater than that 
maintained at its terminals unless a static charge be 
given. 

Such a conductor or condenser is said to have a ca- 
pacity of one farad, when a charge of one coulomb 
produces a difference of potential of one volt. This 
unit comes into use very seldom in ordinary work. 

THE JOULE 

The joule is the unit of work. It is equal to the 
energy expended in forcing one ampere through a re- 
sistance of one ohm, in one second. This unit is also 
seldom used. 

THE WATT 

The watt is the unit of power. Just as the ampere 
expresses the rate of current flow, without telling us 
anything about the actual quantity delivered, so the 
watt measures the rate of doing work, or the rate of 
energy consumption in the circuit. The watts in any 
circuit are equal to the volts multiplied by the am- 
peres. An incandescent lamp requiring 110 volts and 
Vo ampere is said to consume energy at the rate of 
55 w^atts. Seven hundred and forty-six watts equal 
one horsepower. The watt is a much used unit and 
charges for use of light or power are usually based 



18 Operating and Testing 

upon watt-hours. The watts supplied, multiplied by 
the time, measure the power delivered. 

THE HENRY 

The henry is the unit of induction. It is seldom 
used in ordinary practical calculations but an under- 
standing of its meaning is important. 

The henry represents the induction in the circuit 
w^hen the induced electro-motive-force is equal to one 
volt while the inducing current varies at the rate of 
one ampere per second. 



CHAPTER III 

MAGNETISM 

The simplest form of magnet and also the one with 
which people are most familiar is the compass needle. 
This needle is merely a bit of magnetized steel and 
has the property of pointing toward the north with 
one of its ends and, of course, south with the other. 
Such a compass needle is a very convenient instru- 
ment to have about and many instructive little ex- 
periments can be made with it. If we take a compass 
and explore any piece of steel that has been lying in a 
north and south direction, as, for instance some por- 
tion of a steel building, we shall quickly see that the 
north end of the piece of steel has a tendency to repel 
the north seeking end of the needle, but will attract 
the south seeking end of the same needle with as 
much force as it repelled the other end. In making this 
experiment and in all other similar experim^ents care 
must be exercised not to bring the needle, especially 
if it should not be free to swing, too close to the bar 
of steel, if this be strongly magnetized, otherwise the 
powerful magnetism of the bar may overpower that 
of the needle and reverse its polarity. In such a case 
the former north seeking end would become the south 
seeking end, 

19 



20 Operating and Testing 

^'e have mentioned the needle and the bar as being 
made of steel because steel diffei-s from iron in that it 
has the power to retain whatever magnetism it may be 
charged with for an indefinite time, while iron, espe- 
cially if it be well annealed and soft, looses its mag- 
netism the instant the magnetizing force ceases to act. 
A bar of iron will attract the needle as well as the 
steel but to a lesser extent : with the steel bar the at- 
tracting or repelling force will be due to the action of 
both magnets while with the iron bar it will be only 
the force of the needle that does the attracting. 

Magnets consisting of hardened steel are known as 
permanent magnets and usually made up either in 

>: sx s^rsx s 




Fisrure 3 



C5 



horse-shoe shape or in the form of straight bars as 
shown in the following figures. It is impossible to 
make a magnet with one pole only. Xo matter into 
how many pieces we may divide a magnetized bar. 
each piece will possess a north and a south pole. This 
is illustrated in Figure 3 where the different poles are 
designated by the iron filings which cling to them. If 
these pieces be all joined again perfectly the inter- 
mediate poles will all disappear and there will be only 
the two poles, one at each end. It is, however, possi- 
ble to arrange a bar magnet so that it shall have a 
number of poles throughout its length, even while it 
remains solid. This is illustrated in Fisrure -i. where 



Magnetism 21 

the two ends of the bar are magnetized in opposite 
direction so that two poles of same sign are formed in 
the center and oppose each other. 

Consider now the horse-shoe magnet shown in Fig- 
lU'e 5. If we take a magnet of this kind and sprinkle 
a lot of iron filings or small tacks about the ends they 
will be attracted and form around it in the manner 
shown. If the magnet is weak it will be necessary to 
assist the formation somewhat by gently placing the 
tacks where they will.stick. If we now raise the mag- 
net, a large part of the tilings or tacks will follow 
and we can carefully put on a number more, but shall 
soon learn that there is a limit and that as we put on 




Fiofure 4 



o 



more tacks in one place some of the others will fall 
off. If we now take the armature A and place it 
across the pole of the magnet, say at 0. by far the 
greater part of the tacks will fall off. The reason for 
this is that the magnetic flow or flux, as it is usually 
termed, follows along the lines of least resistance like 
any other flow. The armature offering a path of 
much lower resistance than the partially disconnected 
tacks simply shunts the flow around them and they 
cease to be attracted. 

The magnetism is conceived to consist of a flow of 
lines of force as indicated in Figure 6. These lines 
are supposed to leave the magnet at the north pole X 



22 



Operating and Testing 



and passing through the intervening space, to return 
to the south pole S of the same magnet. If we take 
a compass and beginning, say at the right hand end, 
move the needle along the path of the lines of force 




Figure 5 

we shall see it align itself to them and as it is brought 
to the other end of the bar the other end of the needle 
will meet it. The flow of these lines of force is greatly 
facilitated by iron or steel but there is no medium 









/ / 







Figure 6 



/ / /> 



\ \ 



which can be interposed that will prevent the flow en- 
tirely ; in other words, there is no insulation for mag- 
netism. It is, however, possible to shield bodies from 
it by introducing an easier path for it a^ we have seen 
in the experiment with the tacks. 



Magnetism 23 

Permanent magnets are generally made by ^'touch- 
ing/' that is, a magnet is wiped across the end of the 
bar which is to be magnetized as shown in Figure 7. 
If the inducing magnet is strong it is not even neces- 
sary to bring it in contact with the bar to be magnet- 
ized. One must proceed in a systematic manner, how- 
ever, that is, always touch the same end of the bar to 
be magnetized with the same end of the magnetizing 
bar and move it over the bar in the same direction. If 
this is not done one ' ' touch ' ' will neutralize the other 
and the result will be either no magnetism at all or at 
best but a very little of it. 




Figure 7 

Permanent magnets are often made up of a number 
of bars of equal length and shape fastened together 
and are then known as compound magnets. Perma- 
nent magnets can be demagnetized by heating to a red 
heat. 

ELECTRO-MAGNETS 

Electro-magnets differ from permanent magnets; 
first, in being made of soft iron instead of steel ; sec- 
ond, the magnetizing force is not another magnet, but 
a current of electricity ; third, the magnetism lasts only 
while the current is circulating in the wire wound 



24 Operating and Testing 

around the core ; fourth, the strength of magnetism is 
variable and within certain limits in proportion to 
the current flowing; fifth, the polarity, or the direc- 
tion of the lines of force changes with the direction of 
the current and can therefore be instantly reversed. 

"We may now consider the generation of magnetism 
by means of the electric current. 

If we assume the black circle (Figure 8) to be an 
electrical conductor in which the current is flowing 
in the positive direction (i. e., away from us) that 
conductor will be surrounded by lines of force circling 
about it in the direction of the arrows shown. The 
number of lines of force will be directly in proportion 







Figure 8 Figure 9 Figure 10 

to the current strength (number of amperes) in the 
circuit. If we reverse the direction of the current the 
lines of force will circulate in the opposite direction. 
If we lay two wires, carrying current in the opposite 
direction, side by side as shoA\Ti in Figure 9 the lines 
of force will repel each other and tend to separate the 
wires ; if, however, these wires be carrying current in 
the same direction the lines of force will act in har- 
mony and tend to draw the wires together as in Figure 
10. These lines of force are, of course, only concep- 
tions, but they are very natural ones. If wires such 
as those shoAATi be thrust through a piece of paper or 
cardboard at right angles to it and if iron filings be 



Magnetism 25 

sprinkled on the paper and near the wires, these filings 
will have a tendency to arrange themselves in circles 
around the wires as outlined in the figures. In order 
to properly get such an online it will be necessary to 
gently jar the paper several times thus temporarily 
annulling the friction which tends to hold them in 
their place, so that they may more readily align them- 
selves to the lines of force surrounding the wire. 

If we now^ wrap a wire carrying a current of elec- 
tricity around a bar of iron as shown in Figure 11 
these lines of force will pass through the iron as de- 
picted and we shall have a similar circulation of lines 
of force in this case as was observed in a magnetized 




Figure 11 

bar of steel. Magnetism is also produced by a coil of 
wire wound in this way that contains no iron but the 
magnetic flux will be much less. This is due to the 
fact that the iron offers a much lower resistance to 
the flow of lines of force than does air and hence 
their number is greatly increased. The law that gov- 
erns magnetic flux is exactly similar to Ohm's law 
which governs current flow It is : 

Magneto-motive force 
Magnetic flux = 



Magnetic resistance 



The magneto-motive-force is produced by the cur- 
rent circulating in the coil of wire and so far as mag- 



26 



Operating and Testing 



netism is concerned it matters not at all whether the 
100 amperes circulate once around the bar or certain 
air space or whether one ampere circulates 100 times. 
The magnetizing force is always proportional to the 
product of the number of turns of wire and the cur- 
rent flowing in the wire. This product is generally 
known as the ^* ampere turns." 



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Figure 12 

The magnetic resistance varies with the material 
used inside of the coil, or helix, as it is often termed. 
It is greatest with air (with exception of a few sub- 
stances that need not be considered in practical w^ork) 
and least with well annealed wrought iron. The mag- 
netic resistance also decreases as the cross-section of 
the iron increases and, conversely, increases as the 
cross-section of the iron decreases, i. e., the core be- 



Magnetism 27 

comes smaller. The above is rigidly true only for 
air and approximately only within certain limits for 
iron. The conductivity of iron for lines of force 
has a limit and if we attempt to force too many lines 
of force through a given core a point will soon be 
reached where the iron assists the magnetization only 
to a very small extent and any further increase in the 
strength of that magnet will be little more than in 
the ratio that is possible for air. This is illustrated 
by Figure 12 which shows graphically, by means 
of the curves the relative magnetism produced in dif- 
ferent kinds of iron and steel. The highest magnet- 
ization is possible with annealed sheet iron, the lowest 
curve shown is for cast iron. The numbers along 
the bottom line indicate the relative ampere-turns or 
magnetizing force and those along the vertical line 
the resulting magnetic flux or magnetism. 

"We have seen by Figure 11 how the lines of force 
produced by currents of electricity produce magnet- 
ism, either in the surrounding air or in a bar of iron. 
If we now coil another wire about the bar and send 
current through it in the opposite direction, or reverse 
a part of the winding in any coil so that current will 
circulate in the opposite direction w^e shall neutralize 
the influence of the first coil; that is, the lines of 
force produced by the two windings will oppose each 
other and there will be no magnetism if they are ex- 
actly equal to each other. If they are not equal then 
the resulting magnetism will be proportional to the 
difference in strength of the two opposing coils. It 
must not be understood that the number of turns of 
wire, size of wire, and current in the wire must be the 



28 



Operating and Testing 



same, but that the ''ampere turns'' in ine two coils 
must be equal. To find the difference we must sub- 
tract the ampere turns in the weaker coil from those 
in the stronger. It is not possible to quite neutralize 
the action of one coil by the action of the other but 
we can come very close to it and the remaining mag- 
netism can be detected by the most delicate instru- 
ments only. Such a winding is known as ' ' differen- 
tial'' and is made use of in many dynamos, motors, 
arc lamps, measuring instruments, etc. 

AVe may now briefly consider the forms of magnets 
suitable for different purposes. The attraction of an 







] N []| J], 


I 







Figure 13 

electromagnet for its armature varies as the square 
of the number of lines of force passing through both. 
If then Ave desire to obtain the greatest traction, we 
must see that we obtain the greatest number of lines 
of force that a given current can produce. For this 
purpose it is necessary to arrange the magnetic cir- 
cuit so that it shall have the least possible resistance. 
This we obtain when we make the cross-section of the 
core large enough so that the magnetization need never 
be pushed beyond the nearly straight rise of the curves 
shown in Figure 12. The iron core should also be 
made as short as possible. We must, however, have 
space to place a certain number of turns of wire 



Magnetism 



29 



around the core and it must be long enough to allow 
this. It need not be a bit longer. We must not, 
however, imagine that very much can be gained by 
crowding the windings together as shown in Figure 
13, for in such a case the outer layers of wire become 
very long and introduce unnecessary resistance into 
the electrical circuit and also, this construction makes 
necessary an unusual length of the yoke. As a gen- 
eral rule it will be found advisable to make the thick- 
ness of the coil about equal to the thickness of the core ; 
to make the yoke just long enough so that the coils 




Figure 14 

will not interfere with each other when they are being 
placed in position and to make the core long enough 
to accommodate the necessary wire. 

In Figure 14 we have shown a cross-section 
through an electromagnet showing the windings sur- 
rounding the iron and a general scheme of the lines 
of force existing in such a magnetic circuit. The 
armature is shown out of contact with the magnet and 
there is also indicated a considerable leakage of lines 
of force. If the armature is brought dowTi in contact 
with the core it will have a double effect upon th<^ 



30 



Operatijig and Testing 



lines of force; first, these lines will be increased in 
number because the resistance of the magnetic cir- 
cuit has been lowered; second, because the leakage 
also is very much reduced. Reasoning from these 
facts we can readily see that the best proportions for 
the limbs of a magnet depend somewhat upon the use 
it is to be put to; whether the armature is to work 
close to the core, i. e., if the range of action is to be 
small the tendency to leakage will be small and we can 
let the poles of the magnet come reasonably close to- 




Figure 15 



gether and make the magnet very short, but if the 
range of action is to be long w^e mast separate the 
poles more and make the cores longer so as to lessen 
the tendency to leakage. 

Different arrangements of the magnetic circuit are 
also necessary to provide for different speeds of action. 
The solenoid. Figure 15, has a very long range of 
action, it tends to pull the core C up into the coil but 
this action is, on the whole, very slow and not very 
sensitive to small currents. 



Magnetism 



31 



Figure 16 shows a type of magnet that is very 
sensitive to small currents. The main yoke is a- 
compound permanent magnet consisting of a number 
of pieces of magnetized steel fastened together. On 
the ends of these permanent magnets are fastened 
soft iron extensions and on these the magnetizing coils 
are wound. This form of magnet was invented by 
Prof. Hughes for use with a printing telegraph and 
means were provided to bring the armature tight 
against the poles where it would stick, held by the 





Figure 16 

magnetism of the steel bars which also magnetized 
the soft iron ends. It was the function of the elec- 
tric current circulating in the coils around the soft 
iron extension to oppose or neutralize this magnetism 
and thus release the armature. In this way the arma- 
ture could be very quickly controlled and with very 
small currents. 

For quick action the magnetic circuit should not 
be too good. The cores should be short, the winding 
extra thick upon them and the air gap between the 



32 



Operating and Testing 



cores and the armature considerable. If the armature 
comes in contact with the cores the demagnetization is 
greatly retarded as this helps increase the hysteresis, 
of which we shall speak later. 

A special form of magnet that is often used is dia- 
grammatically shown in Figure 17. In this form 
of magnet the armature A is continually under the in- 
fluence of the permanent magnet M. "While current 
is passing through the coils in one direction one of 
the cores will attract the armature and the other w411 
repel it. If the current in the coils is now reversed 




the magnetism will also be reversed and the armature 
thrown the other way. The end that before was at- 
traicted will now be repelled and the one that before 
was repelled will now be attracted. Under the influ- 
ence of an alternating current the armature will move 
in time with the current and cause the bell to ring 
as long as the current flows. This form of magnet is 
also very sensitive and such a bell and all apparatus 
of this kind is known as ^^ polarized.'' 

The cores for alternating current magnets require 
to be laminated and thoroughly annealed. A lami- 
nated core is made up of a number of thin plates as 



Magnetism 



33 



in Figure 18. The core is subdivided in this way 
as otherwise currents would be induced in the iron 
and these currents would heat the iron and cause con- 
siderable waste of energy. The oxidization on the 
plates introduces sufficient resistance to prevent the 
circulation of such currents. 

There is another source of heating of alternating 
current magnets and this is kno\\TL as * ^ hysteresis. " 




Figure 18 

Every piece of iron has a tendency to retain some of 
its magnetism and this magnetism must, when the 
direction of current is changed, be dispelled. This ef- 
fect is small with very good annealed iron but quite 
great with inferior iron or steel. 

There is also assumed to exist a sort of friction be- 
tween the molecules of iron of which every bar con- 
sists and that, with changes in magnetization these 
molecules are forced to align themselves in a different 
manner ; thus if these changes are rapid and continu- 



34 



Operating and Testing 



ous the friction of the molecules will also cause the 
iron to heat. 

Figure 19 shows the waste of energy due to resid- 
ual magnetism of different kinds of iron and steel. 













1 












i. tf lj;2Jr 


^^ 




— ~~ 








=■ 
























is 


r 




^ 


^ 


^ 




^ 
























^ML^ 


^ 


t^^^ 
*^« 


p 


^ 
































^^l^&^w^^^ 


Km 


































/ 


' IL 


1 ^ 




































m 




, / 




































/fn. 


fl 


M 
































^ 




— 


'JUr^ ^>^^ 


f 


































^ 


r 


1 


xlP 




































^.„ 




^y 


































j^ 


^:i^4^>I^;mI 


^AM 




































/ 


fa 




w^ 




































^ 


ip 


'Mli 


-1 
































^ 


^%^. 




^ 






























<^ 


^ 


fc^r^ 


^m 


/ 


























..sfiS! 


>i,:^iii 




1 




-J 


--*t^^^ 






\ 






1 













Figure 19 



m. 







Figure 20 

The shaded portion between the tw^o sets of curves 
showing the relative amount of magnetizing energy 
wasted. 

Figure 20 illustrates the molecular friction in an 
iron bar. With each reversal of current the molecules 
are supposed to reverse their positions. 



Magnetism • 35 

WINDING OF ELECTROMAGNETS 

We have seen that currents of electricity circulating 
in the wires wound around an iron core or bar pro- 
duce magnetism and it behooves us now to learn the 
most advantageous way of applying such currents so 
as to obtain the greatest amount of magnetism from 
a given current. We know from Ohm's law that the 
current increases as the length of the wire in the cir- 
cuit decreases. If then, considering a fixed electro- 
motive force or E.M.F., we wind more coils around 
a given core, the current becomes steadily less as the 
number of turns increases. 'At the same time, how- 
ever, the effect of what current there is increases be- 
cause it circulates around the core oftener. If we 
assume the resistance of the wire around the core to 
be the only one influencing the current w^e shall ob- 
tain the following results. Suppose we have ten turns 
of wire, a resistance of one ohm and a pressure of ten 
volts, this will give us a current of ten amperes and 
consequently a magnetizing force of 100 ampere 
turns. Now double the number of turns, the resist- 
ance will be double and consequently the current only 
5 amperes, but twenty times 5 again equals 100. So 
long as we use the same size of wire it will matter not 
a bit how many turns of wire we take, w^e shall still be 
able to get the same number of ampere turns from the 
same battery unless, how^ever, the length of the wire 
necessary to make a turn increases very much as it 
will if a large number of layers are wound over each 
other. As the current decreases with more turns, 
while the E.M.F. remains constant throughout, it is 



36 Operating and Testing 

evident that we are getting our magnetism with less 
and less expenditure of energy as we put on more 
coils. How much energy it is advisable to consume 
in. producing a certain flow of magnetism depends on 
circumstances. If power is cheap we can use a few 
turns of wire and a large amount of current, if it is 
dear we shall find it to our advantage to provide more 
windings and thus save energy. 

The determining factor of the winding is, however, 
not alone the amount of energy we are willing to ex- 
pend in the coils, but the temperature we are allowed 
to maintain. The magnetism created in any coil in- 
creases directly as the current but the heat generated 
increases as the square of the current. If in any coil 
we double the current we double the magnetism and at 
the same time increase the heating four-fold. The 
heating of the wires must therefore never be lost 
sight of. 

Let us examine now how a change in the size of wire 
affects the economy of winding. If we take a coil 
containing say 100 turns of wire and place in the same 
space a wire of half the diameter of that of the first 
coil (neglecting differences that may be caused by va- 
riations in the relative thickness of the insulation) 
we shall obtain four times as many turns and the ware 
will have but one fourth of the cross-section of the 
former. Its total resistance will therefore be sixteen 
times as great as that of the old coil and from the 
same voltage it will receive but one sixteenth of the 
current; there will be, however, four times as many 
turns and the magnetizing force will therefore be one 
fourth that of the old coil. As the current is here 



Magnetism 37 

but one sixteenth of the former the energy expended 
per ampere turn will be but one fourth of the former. 
In this case again we receive from the energy ex- 
pended per watt, a much greater amount of magnet- 
ism, but in order to get the same total amount w^e 
must increase the E.M.F. in proportion to the in- 
creased resistance divided by the increased number 
of turns, in this case sixteen divided by four. 

"We cannot always assume, however, that the coils 
of the magnet are the only resistance in the circuit. 
This would apply very well to the field coils of dy- 
namos or the regulating coils of arc lamps, but not at 
all to telegraphy for instance. Here the magnets are 
long distances apart and far from the source of cur- 
rent and economy demands the use of small wires and 
these have high resistances. In such cases only a part 
of the energy is expended in the magnet coils. To 
illustrate the most advantageous winding of magnet 
coils for these conditions, let us assume the follo^A^ng 
case. Suppose we have an E.M.F. of 100 volts, a line 
resistance of sixteen ohms and a magnet which is 
wound with 100 turns of wire which just fill out the 
space allotted to the coils and Avhich have a resistance 
of one ohm. This gives us a total resistance of 17 
ohms and with 100 volts we therefore obtain very 
nearly 6 amperes making, 6 times 100 or 600 ampere 
turns. The energy consumed in this case will be about 
600 watts. If we now try a wire of half the diameter 
of the former we shall in the same space have 4 times 
as many turns and each turn having only 14th the 
cross-section will have 4 times the resistance, so that 
the total resistance of the coil will be 16 ohms and the 



38 Operating and Testing 

total of line and magnet 32. Our current will now be 
about 3.2 and give us 1280 ampere turns. The en- 
ergy (in watts) consumed is now 320. For a third 
trial let us again take a wire of half the diameter of 
the former. The number of turns will now be 1600 
and the resistance of the coil 256 ohms, giving us a 
total resistance of 272 and a current of about .4 am- 
peres and a total of 640 ampere turns. The energy 
consumed in this case will be only 40 watts. Similar 
results will be obtained with all variations in diameter 
of wire and an inspection of these results will illus- 
trate to us the rule, by which most designers of mag- 
nets for such work are guided, which is: make the 
resistance of the magnet coils in the circuit equal to 
the resistance of the line. If there are many magnets 
their combined resistance is made equal to that of the 
line. It must be understood of course that only cop- 
per wire of the highest conductivity should be used. 



CHAPTER IV 

PRINCIPLES OF DYNAMO-ELECTRIC MACHINES 

The dynamo consists of two main parts, one of 
which is a hnge electro-magnet, in the simpler forms 
approximating closely in shape to the horse-shoe mag- 
nets with which we are familiar. This magnet in the 

A 




Figure 21 

dynamo is known as the 'Afield magnet" and is often 
spoken of merely as ^Hhe fields." In the simpler 
forms of generator these fields are usually stationary. 
The other part of the dynamo is known as the arma- 
ture. In all machines in which the fields are station- 

39 



40 Operating and Testing 

ary the armature is made to revolve. In Figure 21 
the fields of the dynamo are designated by the letter 
M and the armature by the letter A. Upon the iron 
core of the fields are always wound a number of turns 
of wire as upon any electro-magnet, and in this wire 
currents of electricity circulate, producing lines of 
force, just as in the different types of electro-magnets 
we have discussed in the previous chapter. 

In the dynamo the electro-motive-force is developed 
by '^cutting'' lines of force. Lines of force are said 
to be ^^cuf when a conductor of electricity is moved 
in a magnetic field in a direction at right angles to 
the lines as indicated in Figure 22. Such a field is 
shoAvn in Figure 22 between S and N and if the bar 
be moved through this field at right angles to the lines 
of force an E.M.F. proportional to the number of lines 
of force cut per second will be generated. No current 
will be generated in the bar as shown as it does 'not 
form, an electrical circuit; but the fact that an E.M.F. 
exists could be readily shown by connecting a volt- 
meter across the ends of the bar. The direction of the 
flow of current generated depends upon the direction 
in which the lines of force are cut. By reversing the 
direction of motion of the bar, or by reversing the di- 
rection of the lines of force, i. e., reversing the current 
which produces them, the direction of the flow of cur- 
rent in the bar will be reversed. 

The direction of the flow of current induced in any 
moving conductor may be determined by the following 
method : Place the thumb and first two fingers of the 
right hand in such a position that each forms a right 
angle with the others as shown in Figure 23. If the 



Principles of Dynamo-Electric Machines 41 

thumb points in the direction of motion of the moving 
wire and the first finger in the direction of the lines 
of force, or from the north to the south pole of the 
magnet, the third finger will point in the direction of 
the flow of the induced current. 

If the bar in Figure 22 is moved slowly the E.M.F. 
generated will be but small. If the number of lines 
of force remains constant, the E.M.F. will be directly 
proportional to the speed with which the bar is moved. 
If the speed of the bar remains constant the E.M.F. 




1' 1 



Figure 22 



Figure 23 



will vary directly as the lines of force vary. "We can 
therefore raise or lower the E.M.F. of any dynamo by 
varying either the speed of the moving conductors or 
the intensity of the magnetization of the fields or by 
both. 

An E.M.F. of one volt is obtained for every 100,- 
000,000 lines of force cut per second. If therefore 
the gap in the iron of the fields has a cross-section of 
100 square inches, and the magnetization is equal to 
20,000 lines per inch, the bar would have to cut 



42 



Operating and Testing 



through this field 50 times per second to generate an 
E.M.F. of one volt. 

The generation of E.M.F. in this way is kno\\Ti as 
electro-magnetic induction. 

Figure 24 represents a coil of wire the ends of 
which are connected to the two collector rings 1 and 
2. Brushes bearing upon these collector rings con- 
nect the coil to the external circuit C. If now this 
coil of wire were revolved around an axis indicated 
by the dotted line through the center of it and in the 




Figure 24 

magnetic field, it would generate a current which 
would manifest itself in the outer wires C, either by 
heating them or by its effect upon instruments we 
may place in the circuit. We can get a clearer idea 
of the nature of this current and the laws governing 
it by reference to Figure 25 which shows an end view 
of the same coil of wire. 

Let the points 1 1^ represent opposite sides of the 
coil and let them revolve at a uniform rate of speed ; 
they will then successively move to the points 2 2^ ; 
3 3^ ; 4 4^ until 1^ is at the point now occupied by 



Principles of Dynamo-Electric Machines 43 

1. The wires will in this time have made one half 
revolution. We have seen that the E.M.F. generated 
is proportional to the rate of cutting lines of force. 
We can see by an inspection of Figure 25 that the 
rate of cutting lines of force is not uniform, for at 1, 
for an instant the wire is moving practically parallel 



Figure 25 

to them and is not cutting any. Also during % ^^ 
one revolution from 1 to 2 it is not cutting nearly as 
many lines as during the time it travels from 2 to 3. 
In fact while the wires are at the exact points 1 1^, no 
E.M.F. is generated, but as they pass this point it 
begins gradually to rise until 1 is at 3 when it begins 




Figure 26 

gradually to fall until 1 is at 1^ when it is again at 
zero. When 1 has passed the point now occupied by 
11 the E.M.F. again begins to rise but in the opposite 
direction, for the lines of force are now being cut in 
the opposite direction. The rise and fall of E.M.F. 
or current in an armature coil operating in this man- 



44 Operating and Testing 

ner can be illustrated by mean of ^^ curves" as s1io\\ti 
in Figure 26. Everything above the neutral line N 
being taken as representing E.M.F. in one direction 
and everything below as in the opposite direction. 
These curves show us also that the currents actually 
generated in a dynamo-electric-machine are alternat- 
ing in direction and variable in strength. Alternat- 
ing currents are not, however, always desirable and 
it becomes necessary to rectify them so as to obtain 
continuous or direct currents. For this purpose a 
commutator is provided. 




Figure 27 Figure 28 

The nature and general construction of the commu- 
tator can be seen from Figure 27. It consists in these 
simple cases of two sections of copper connected to 
the terminals of the coils arranged as an armature. 
If the coil equipped with such a commutator is now 
revolved, it will be seen that just at the time when the 
open section of the commutator is in line with the 
dotted line in either one of the figures, the brushes 
B, Avhich bear upon the commutator and connect it 
with the exterior circuit are in a position to change 



Principles of Dynamo-Electric Machines 45 

from one section to the other. If the brushes are prop- 
erly set this will occur at the precise moment when 
the coil is at the point w^here it is generating no cur- 
rent as in Figure 27. This is the point at which the 
current in the armature (coil of wire between the pole 
pieces) changes in direction. 

The current in the armature continues to alternate, 
i.e., change in direction, at every half revolution, but 
by means of the commutator the coils are disconnected 
from one side of the external circuit and connected 
to the other so that the current in the exterior circuit 
remains always in the same direction. The E.M.F. 
or current generated by an armature containing only 



Figure 29 

one or a few turns of wire like the one shown would 
still produce a pulsating current and this current 
would be represented by such curves as are shown in 
Figure 29. These currents are all in one direction 
but vary in strength from zero to the maximum of 
which the machine is capable. 

It will be noticed that the brushes, during the mo- 
ment they are changing from one commutator seg- 
ment to the other, are in contact with both of them* 
It could of course be arranged to avoid this by mak- 
ing the brushes narrow and the space or insulated 
material between the two segments wide so that the 
brushes would leave one section before they came in 
contact with the other. This would, however, cause 



46 Operating and Testing 

an opening of the circuit every time the armature 
made a half revolution and would result in very un- 
satisfactory lighting and motor service besides caus- 
ing very annoying and destructive sparking, as every 
break in an electric circuit is accompanied by an arc 
which rapidly eats away copper and insulating ma- 
terial. The brushes connecting together the two seg- 
ments, it will be seen by inspection of Figure 27, cause 
the coil to be on short circuit during the time that the 
brush is in contact w^ith both of them. If this hap- 
pens w^hile the coil is in a position w^here it is not gen- 
erating any E.M.F. and consequently no current is 
flowing no harm will be done ; but if this occurs at a 
time when the coil is in an active part of the field 
and generating, a very considerable current will cbe 
produced because the resistance of such a coil is 
usually very low. This current w^ill heat the Tv^re 
and cause considerable waste of energy, — energy that 
should appear in the external circuit, but now does 
no useful work. Aside from this waste of energy and 
troublesome heating of the armature, w^hen the brush 
breaks contact with one of the segments, this current 
will be broken and manifest itself in the form of a 
spark which, recurring often, will quickly destroy the 
commutator. 

Not only this, but the commutator, if the position 
of the brushes is very wrong, as in Figure 28, would 
fail of its purpose and not rectify the current at all. 
With a single coil and the brushes set as in Figure 28 
the current w^ould be graphically represented by 
curves such as shown in Figure 30, it would still be 
an alternating current changing in direction in an 



Ppmciples of Dynayno-Electric Machines 47 

irregular way. In practice armatures do not consist 
of a single coil and only in very exceptional cases 
would these considerations in the extreme form apply. 
The commercial armature has a greater number of 
turns of wire and for bipolar, or the simpler machines, 



Figure 30 

is made up either as shown in Figure 31 or diagram- 
matically in Figure 32 which is known as the gramme 
ring type of armature, or as shown in Figures 33 and 
34 which is known as the ^^drum^' armature. 




Figure 31 

By reference to Figure 32 we can continue our 
study of the armature in. a more commercial form. By 
noting the position of the brush B we can see that it 
is about to short circuit the coil connected to the two 



48 



Operating and Testing 



segments to which it is nearest. This coil is, however, 
only a small part of the whole and a wrong placing 
of the brushes would not have the effect outlined be- 
fore in regard to armatures having but one coil. No 
matter how the brushes may be set, they short circuit 
only one coil each and therefore only a small part of 
the current is ever broken or changed in direction at 
one time. As the resistance of such a coil is, however, 




Figure 33 

very low the current generated in it is, if it is in an 
active part of the field at the time, quite sufficient to 
cause trouble, which usually indicates itself by more 
or less severe sparking. If the coil is located in the 
neutral part of the field as that of Figure 32, for in- 
stance, there will be no sparking. The smaller each 
individual coil is made the easier it becomes to realize 
this condition and for this reason dynamo armatures 
are generally made up of a large number of coils, and 



Principles of Dynamo-Electric Machines 49 

of course a corresponding large number of commuta- 
tor segments. 

The position of the brushes also has a great deal to 
do with the E.M.F. generated by the dynamo. To 
comprehend this let us again refer to Figure 32. The 
lines of force are parsing through the fields and ar- 
mature in a certain direction, from N to S. We know 
that the direction of the current depends upon the 
direction in which these lines are cut by the wires. 
As the armature is revolving always in the same direc- 
tion those lines at S are cut in an opposite direction 




Figure 33 

from those at N, consequently the currents generated 
in the two halves of the armature are flowing in a di- 
rection towards each other; this causes them to meet 
at the positive brush, flow out through the circuit and 
return to the negative brush, dividing again in the 
armature. In this way it can readily be seen that 
the two halves of the armature are in parallel. Now 
let us move the brush one section forward. Before, we 
had two coils in the neutral part of the field, generat- 
ing no current, and three coils under the influence of 
each field doing active work. Now we have still two 
coils in the neutral field, idle, and the currents in each 



50 



Operating and Testing 



direction are generated by two coils under the influ- 
ence of each field and one under the influence of the 
the other ; but this latter coil is not generating in har- 
mony with the other two, it is actually opposing them 
as it is under the influence of the opposite field. This 
position of the brushes is therefore not only the cause 
of much sparking but also reduces the voltage of the 
dynamo. By shifting the brushes, forward or back, 

/ 




Figure 34 

until they are at right angles to the neutral line the 
voltage can be reduced to zero. If the brushes are 
shifted still farther the voltage will again begin to 
rise but in the external circuit current will be in the 
opposite direction. 

In present day practice the brushes are used to reg- 
ulate the voltage of dynamos only in exceptional cases 
which will be considered in another chapter. The 



Principles of JJynaino-Electrio Machines 51 

necessary regulation is almost invariably brought 
about by means of a variable resistance or ' ' rheostat. ' ^ 
Such a rheostat is cut into the field circuit of a dy- 
namo as shown m Figure 35 which shows a diagram 
of a simple shunt dynamo, A being the armature, F 
the field wires, R the rheostat and L the exterior or 
lead wires of the dynamo. "When the machine is in 
operation current circulates around the fields and 
through the wires of R. The arm of R is a conductor 




wmMMmv 

Figure 35 

and is movable. In the position shown the current 
in the wires must traverse the greater part of the 
wires in R. If the arm of R, however, is moved to 
the left it gradually cuts out coil after coil until when 
it arrives at the last notch all of the resistance of R is 
out of the circuit. The resistance of the circuit is 
then at its lowest and consequently the current at 
its highest value and the field the strongest. By mov- 
ing the arm in the opposite direction we cut more re- 



52 



Operating and Testing 



sistance into the circuit and thus weaken the fields of 
the dynamo. 

By moving the bar in the proper direction Ave can 
therefore increase or decrease the current strength in 
the fields a-nd thus change the number of lines of force 
in the armature and these in turn (speed of armature 
remaining unchanged) will govern the E.M.F. of the 
generator. 

The current flowing in the external circuit depends 
upon the E.M.F. and the resistance in the circuit. 
The current is* all generated in the armature and of 




-"^ 






^j:^ 




^ 4tf 



Figure 37 



Figure 36 

course all passes through it. And this current also 
makes a magnet out of the armature and the resulting 
magnetism opposes the magnetism of the fields to a 
certain extent as we shall see by reference to Figure 
36. We can determine the direction of current in an 
armature by the following rule which has already been 
given but is repeated here for convenience of the stu- 
dent. Grasp the north pole of the d^Tiamo with the 
right hand arranged as in Figure 23. Let the index 
finger point in the direction of the lines of force and 
the thumb in the direction of motion ; the middle fin- 



Principles of Dynamo-Electric Machines 53 

ger will then point in the direction the current is said 
to be flowing. AYith condition as shown in Figure 
36 the current will be flowing around the armature as 
indicated by arrow points. Current flowing in this 
direction will produce lines of force in the armature 
as indicated by the other arrow points. It will be 
noted that these lines of force oppose those coming 
from the N pole to a certain extent. As lines of force 
can never intersect each other the result of this op- 
position is that the lines of force which pass through 
the armature and induce poles in it as shown in Fig- 
ure 37 while no current is flowing in the armature, are 
deflected to a certain extent as shown in Figure 36. 

Figure 36 shows the counter-magnetization of the 
armature which results in deflecting the lines of force 
from the fields somewhat in the direction of motion of 
the armature. In actual practice the lines of force 
from the fields reverse those of the armature but are 
deflected by them and the general trend of the result- 
ant lines of force is indicated by the curved line F, 
Figure 36. 

The neutral point or point at which the brushes 
must be set for least sparking is therefore no longer 
in the center between the two pole pieces as in Figure 
37, but is shifted somewhat in the direction of motion 
of the armature as in Figure 36. If we reverse any 
one of the conditions the current will be reversed but 
the same relation between shifting of the neutral point 
and direction of motion will always hold. The coun- 
termagnetization of the armature increases as the cur- 
rent increases and therefore it becomes necessary to 
shift the brushes in the direction of motion as the load 



5-i Operating and Testing 

increases and in the opposite direction as the load 
decreases. 

It is evident that this shifting of the brushes which 
becomes necessary' when the current flow in the d^Tiamo 
changes, depends almost entirely upon the relative 
strength magnetically of the fields and armature. If 
the machine is so constructed that the magnetism of the 
armature is very strong, then, as the current increases 
the magnetism will increase and greatly shift the neu- 
tral line and make necessary considerable shifting of 
the brushes. But if the fields are very strong com- 
pared to the armature the latter will have but little 
effect and but a very little shifting of the brushes will 
be necessary. 

In connection with chTiamos two terms are often 
used erroneously as having the same meaning. These 
terms are electro-motive force or E.M.F. and differ- 
ence of potential or P.D. for short. Strictly speaking, 
the term E.^M.F. refers only to the greatest difference 
of potential the machine or battery can produce and 
this P.D. can exist only while an infinitesimally small 
current is flowing. AVhenever any appreciable cur- 
rent is flowing there is always a loss of potential 
which is always equal to IXR- To get the maximum 
voltage of a d^Tiamo we must therefore arrange that 
no current except that through the voltmeter be flow- 
ing. In a poorly constructed armature the difference 
between E.M.F. and difference of potential is consid- 
erable. 

Aside from the foregoing there are many other 
points about dATiamos that require explanation but 
these can more readilv be treated in connection with 



Principles of Dynamo-Electric Machines 55 

the particular type of machine in which they are of 
greatest importance. 

In general a good dynamo has a large number of 
commutator sections. (To avoid sparking.) A mag- 
netically weak armature and strong fields. (To avoid 
shifting of brushes.) The fields are wound with many 
turns of fine wire. (To save energy. See chapter on 
magnetism.) A small air gap between fields and ar- 
mature. (To prevent leakage and unnecessary mag- 
netic resistance.) The ends of pole pieces not too 
close together. (To prevent leakage around arma- 
ture.) Large wires on armature. (To prevent loss 
of voltage and heating.) 



CHAPTER V 



TYPES OF DYNAMOS 



The oldest type of dynamo is shown diagrammat- 
ically in Figure 38. The use of this type is generally 
restricted to direct current arc lighting. It is known 




Figure 38 

as the series dynamo, the same current passing in se- 
ries, first through the armature, then through the 
fields. Such a machine cannot be used with a vari- 
able current because the strength of the fields would 
be constantly fluctuating. Whenever there would be 
an increase of current strength there would also be 
an increase in voltage and with a decrease in current 
strength there would be a drop in voltage. As the po- 
tential of series arc circuits is generally very high, 

56 



Types of Dynamos 



57 



shunt wound dynamos would require a great length 
of very fine wire and consequently would be ver^^ 
expensive and also very likely to be damaged. This 
is one reason why series dynamos are in special favor 
in connection with series arc circuits. 

The regulation of this type of dynamo always has 
as its object the raising of the E.M.F. as more lights 
are cut into the circuit and a corresponding lowering 
of it as lights are cut out of the circuit, so that the 




Figure 39 

E.M.F. is always at its proper value in regard to the 
resistance of the circuit to cause the necessary current 
to flow. This regulation is generally brought about 
in one of the following ways: By shifting of the 
brushes, by commutation of the fields, or by a com- 
bination of these two methods. 

The method employed of shifting the brushes au- 
tomatically is diagrammatically illustrated in Figure 



58 Operating and Testing 

39. The total d^Tiamo current passes from the posi- 
tive pole of the armature A to the lamps, thence to 
field F, solenoid S and negative pole of dynamo. We 
know that the solenoid has power to control the po- 
sition of the core Avithin it. The stronger the current 
the farther will the core be pulled in in opposition to 
the supporting spring. This core is so arranged that 
with the normal current strength the extension 1 rests 
about midway between the points 2 and 3. If now 
there is a slight increase in current strength, as when 
a lamp is switched out, the core will be draAMi down- 
ward and close an electric circuit at 2. This circuit 
is a shunt to the solenoid and requires but a small cur- 
rent. "When it is closed current passes through the 
clutch 4 and this (by a mechanical contrivance not 
shoAATi) causes the yoke Y to be drawn over so that the 
brushes are shifted in the direction which causes a 
lowering of the voltage and a decrease in current 
strength. As soon as the current goes back to its 
normal strength the circuit at 2 is again open and the 
brushes remain at rest until another change in current 
strength causes the solenoid to change its position. If 
the current becomes too weak the spring draws the 
solenoid up until the circuit at 3 is closed and the 
brushes shifted in the opposite direction by means of 
clutch 5. 

The principle of varying the E.M.F. by field com- 
mutation is illustrated in Figure 40. The automatic 
control is not shoA\Ti and instead hand control is used. 
By moving the lever L to the right or left more or 
less of the field winding can be cut into the circuit. 

Instead of cutting out field coils, a resistance R (see 



Types of Dynamos 



59 



Figure 41) i^ sometimes arranged as a shunt around 
the field coils and as the arm is moved forward or 
back the resistance is increased or decreased, thus tak- 
ing more or less current around the fields and weaken- 
ing or strengthening them accordingly. 

The highest E.M.F. of which the dynamo is capable 
is obtained when the brushes are near the neutral 
point. This position of the brushes can only obtain 
when the maximiun number of lights are in the cir- 
cuit. With a lesser number of lights the brushes must 



f 




Figure 40 

be shifted away from the neutral point sufficient to 
cause a certain number of the armature coils to gener- 
ate in opposition to the rest and thus reduce the 
E3I.F. of the dynamo until the current has its pre- 
determined value. 

From what we have learned in chapter on Principles 
of D^Tiamos it is evident that all d\Tiamos subject to 
such regulation must spark considerably at the 
brushes. There must also be considerable tendencv 



60 



Operating and Testing 



toward heating of armature wire with this kind of 
regulation as some of the coils are nearly always on 
short circuit. This applies also to a great extent to 
machines regulated by field commutation. Machines 
of this type are in consequence usually equipped with 
some special form of commutator calculated to with- 
stand the destructive effects of the arcs formed. In 
the Thomson-Houston dynamo a blower is provided 
which blows out the arc. 

For dynamos of this type the Gramme ring arma- 
ture is preferable because from the nature of its wind- 




VWWWVWWF 



Figure 41 

ing wires of opposite polarity do not cross each other 
as they do in drum armatures. 

Two special types of d\Tiamos very generally used 
for series arc lighting are the Brush and Thomson- 
Houston. 

Figure 42 shows the coils and commutator sections 
of an 8 coil Brush arc dynamo. The diametrically 
opposite coils 1-1 ; 2-2, etc., are connected in series and 
each coil has its own exclusive commutator section. 



Types of Dyn-amos 



61 



By tracing out the circuit from the binish A, it will 
be seen that current enters at this brush, passes 
through coil 1-1 to brush A^ : thence to field H, brush 
B. coils 2 and 4 in parallel, thence to brush B^ and out 
at the positive pole of the d^Tiamo. 

With this armature one coil is always on open cir- 
cuit and the adjustment must be such that this coil 
while open is in the dead part of the field. Each com- 
mutator segment embraces three eighths of a circle. 




Figure 42 

As the different coils are not in series with each 
other but at times in parallel the brushes must be so 
arranged that at no time can a coil that is not gen- 
erating be left in circuit. Such a coil would simply 
form a shon circuit to the line and much of the cur- 
rent that should flow through the line would flow 
through it. By following out in imagination a com- 
plete revolution of the armature one can see that the 
brushes always break contact with the coils as they priss 



62 



Operating and Testing 



out of the influence of the fields. It is very import- 
ant to see that the commutator is always set with re- 
gard to this. 

The Thomson-Houston is another type of open cir- 
cuit dynamo armature. The nature of its winding is 
shown in Figure 43. One end of each coil is con- 
nected to one of the 3 commutator sections and the 
other to a brass ring R common to all the coils. 

A series dynamo if left without regulation will, with 
an increase of current, run its E.M.F. to the maxi- 




Figure 43 

mum of which it may be capable and probably bum 
out. The greater the current the greater will be the 
pressure, but after the fields have become fully sat- 
urated the increase in E.M.F. will be small. Figure 
44 shows the characteristic curve of such dynamos. 
Such curves are obtained by plotting the E.M.F. and 
current existing at the same time on squared paper as 
shown and then combining the points so obtained in a 
curve. This may be to any convenient scale. The 
figure shows only the general autline of such curves 



Types of Dynamos 



63 



as they are of course different with different types and 
design. 

For incandescent lighting, motor service, constant 
potential arc lighting and storage battery work the 
shunt dynamo is much used although of late years the 



'^■ 



i 



amperes 



Figure 44 

compound wound dynamo is crowding it out. Figure 
45 is a diagram of the shunt dynamo. This dynamo is 
generally equipped with a drum armature. It is sel- 




Figure 45 



dom if ever equipped with an automatic regulator and 
instead hand regulation is used. The drop of poten- 
tial at the brushes is equal to the current multiplied 
by the resistance of the armature. In a poorly con- 



64 



Operating and Testing 



structed armature this is considerable so that such a 
machine needs constant watching. An appreciable 
drop in potential is of course accompanied by a weak- 
ened current through the fields which in turn allows 
a further falling off in potential. 

The characteristic curv^e of a shunt dynamo is given 
in Figure 46. If the potential of such a d}Tiamo falls 
off noticeably the fields begin to weaken and thus in- 
crease the falling off in proportion. A shunt dynamo 
if short circuited will for a very short time increase its 
current enormously and will then lose its pressure, the 
short circuit robbing the fields of all current. The 



Figure 46 

curve in Figure 46 shows the effect of an overload 
which is nearly or fully equivalent to a short circuit. 
After the maximum current has been reached the 
pressure falls off so much that the current also de- 
creases and both current and E.M.F. finally return 
to 0. 

As all armatures have some resistance it follows 
that the potential at the brushes of any shunt dynamo 
must fall as the current increases. To compensate for 
this a special winding through which the whole dy- 
namo current flows is put upon the fields in addition 
to the shunt winding. As the drop in potential is 



Types of Dynamos 



65 



always exactly in proportion to the current flowing, 
it is evident that if this current be made to circulate 
the proper number of times around the fields it will 
increase their strength so that the E.M.F. of the dy- 
namo will be raised just enough to make up for the 
loss due to its armature resistance and the E.M.F. 
remain very nearly constant. (See Figure 47.) If 
the current be made to circulate a greater number of 
times the E.M.F. of the armature will go higher 
as the current increases. It is therefore possible to 




Figure 47 

arrange such dynamos to keep the pressure constant 
even at points far away from the machine, but in 
such cases it will go undesirably high at the dynamo 
terminals. 

The characteristic curve of a compound wound dy- 
namo is a combination of the curves of a series and 
shunt machine and sho^\TL in Figure 48. If such a 
dynamo is short circuited the shunt fields will im- 
mediately lose their magnetism but the power of the 
series coils will be momentarily increased as there will 



66 



Operating and Testing 



be for a very short time a great flow of current, due 
to the fact that an instant of time is necessary before 
the magnetism of the fields passes away. If the series 
fields are very strong compared to their own and the 
armature resistance they will energize the fields on 
their own account and the armature will burn out. If 
it is very weak relatively to those two factors, little 
harm will be done if the armature has withstood the 
momentary rush of current which could last only long 
enough for the shunt fields to die down. 

So far we have looked upon all machines as having 
but two poles. Such machines are knowTi as bi-polar. 



Figure 48 

Most of the larger machines are, however, multipolar, 
i. e., equipped with more than two poles. The mag- 
netic circuits and arrangement of pole pieces in a 4 
pole machine are shown in Figure 49. AA^ith such ma- 
chines there is usually a set of brushes for each set of 
poles. The neutral point will be about midway be- 
tween two pole pieces. If the brushes are moved a 
quarter revolution forward or back the directions of 
current will be reversed. Armatures for such ma- 
chines may be wound just as for bi-polar fields but a 
form of winding as indicated in Figure 50 is prefer- 
able. 



Types of Dynamos 



67 



'Figure 50 is a diagrammatic view of the simplest 
form of multipolar armature winding. The wires are 
laid in slots on the outer circumference of the arma- 
ture and are shown as though the armature were cut 




Figure 49 

in two and the wires laid out flat. W, W represents 
the commutator sections and N, S, the poles as in 
Figure 49. 




Figure 50 

A view of a finished armature is given in Figure 51. 

Alternating currents to be available for lighting 

purposes must have quite a high frequency ; 60 cycles 



68 Operating and Testing 

per second or 7200 alternations per minute being 
about the lowest frequency that can be used for arc 
or incandescent lighting without causing annoyances 
through flickerings in light. If such frequencies were 
to be produced by a bi-polar machine it would have to 
operate at a speed of 3600 revolutions per minute. As 
these machines also generally operate at very high 
pressure there would also be, with drum armatures, 
great danger from wires between which great differ- 
ence of potential exists crossing each other. To ob- 
viate the above troubles alternators are usually made 




Figure 51 

multipolar, both, fields as well as armature, consisting 
of a number of sections. 

The alternating current dynamo may have its ar- 
mature stationary and the fields revolving; it may 
have the fields stationary and the armature revolving 
or the fields and armature may both be stationary. 
In the latter case it is described as belonging to the 
inductor type. 

An alternating current cannot be used a^ such to 
excite the field and consequently many dynamos are 



Types of Dynamos 



69 



separately excited by an outside dynamo. Some al- 
ternators, however, are provided with commutators 
which rectify the current and make it available. 

Figure 52 shows the general layout of an alternat- 
ing current dynamo with revolving fields and sta- 
tionary armature. The dynamo is excited by direct 
current from a shiuit dynamo, the current entering at 
D.C. and passing around the fields. The strength of 




Figure 52 

this current can be regulated and through it the E.M.F. 
of the dynamo. 

Every time one of the armature poles passes from 
under one of the stationary poles to the next one there 
is a reversal in direction of the current. 

If supplying a variable load the E.M.F. of the dy- 
namo will be constantly fluctuating, the drop increas- 



70 



Operating and Testing 



ing as the load increases and with this machine there 
is only hand regulation. 

In order to avoid the necessity of constant attend- 
ance and hand regulation alternators are sometimes 
compound wound just as direct current machines. 
The field of such a machine consists of a steady current 
from the D.C. dynamo supplemented by a pulsating 
current from the generator itself. 

In order that the generator current may be used it 




Figure 53 

must be rectified so that, although it is variable in 
strength, the pulsations all pass through the fields in 
the same direction. For this purpose the rectifier R, 
Figure 53, is provided. This rectifier is fastened to 
the same shaft as the armature and revolves with it. 
All of the white sections of R are joined together by 
the w^ires shown as forming a square and the shaded 
by the wires shown as curved lines. The shaded sec- 



Types of Dynamos 71 

tions connect direct to collector ring 2 and the white to 
the wire coming from the armature, as shown. The 
brushes shown bearing upon the rectifier are adjusta- 
ble and are to be set so that at the moment when the al- 
ternating current is passing through the zero part of 
its waves, the connections are changed, i. e., one brush 
changes from a shaded segment to a clear one and the 
other vice versa. By this arrangement the current 
passing through the fields of the generator (stationary 
in this case) remains always in the same direction al- 
though that in the line is alternating. The main cur- 
rent can readily be traced, beginning at A, collector 
ring 1, armature, clear sections of rectifier, fields, 
shaded portion of R to collector ring 2 and the line, 
finally returning to A. The direct current field circuit 
is shown at D C. 

The rectifying arrangement works quite satisfacto- 
rily as long as the load is of constant inductance. 
This is, however, only the case so long as merely in- 
candescent lights are in circuit. When motors or arc 
lights are operated the current does not always co- 
incide in phase with the normal adjustment of arma- 
ture and rectifier and begins either to lag or lead, that 
is, the zero part of the wave occurs a little later or 
earlier and therefore the change of rectifier segments 
is made at a time when there is considerable current 
flowing, which results in severe sparking unless the 
brushes are constantly being shifted. For this rea- 
son the rectifier is not being much used at present. 

It will be seen that by shifting the brushes the full 
width of a segment the direction of the current around 
the fields can be reversed. A variable shunt S can be 



72 



Operating and Testing 



arranged by means of which more or less of the rec- 
tified current can be diverted from the field circuit. 

In actual practice the generating coils of alterna- 
tors are not wound upon projecting coils but laid into 
slots as indicated in Figure 54. Sometimes each slot 
contains only one wire; sometimes there are many. 
The number of slots per pole also varies. For two 
and three phase machines two or three windings are 
arranged either upon the rotating or stationary part. 
In Figure 54 there are three slots per pole and this 
armature is designed for three pha^e currents. The 




Figure 54 

positions of the wires for one of the phases is indi- 
cated by the black circles. As these sweep around 
under the pole pieces the currents induced in each 
w^ire are in a different direction and to make all of 
them generate in series they are connected on the two 
sides of the armature as shown by the heavy black 
lines, w^here the arrows indicate direction of induced 
currents. The other two phases are wound into the 
empty slots in the same manner, and it can be seen 
that while the phase represented by the black circles 



Types of Dynamos 73 

is at a maximum, being directly in the strongest part 
of the field, that at the right of it is increasing and the 
one at the left decreasing. These wires are connected 
to collector rings in such a manner that in the outside 
circuit they are in opposite directions, one wire al- 
ways forming the return for the other two. A partial 
diagram of the winding is shown in the center of the 
figure. 



CHAPTER VI 

PRINCIPLES OF ELECTRIC MOTORS — DIRECT CURRENT 

The reader will, no doubt, have noticed that there 
is no great difference between a dynamo and a motor 
and that there are about as many different types, of 
one as of the other. As a matter of fact, any dy- 
namo can be used as a motor and any motor as a 
dynamo, although as a rule less care is bestowed upon 
the manufacture of motors and most of them w^ould 
operate at very low efficiency if installed as generators. 

In the shunt dynamo we apply power to revolve the 
armature in the fields and the power required is pro- 
portional to the current flowing. If the armature is 
on open circuit we require no more power than is 
necessary to overcome the friction. It is, therefore, 
the reaction of the current in the armature against 
the fields which requires the power to overcome it. 
It follows from this that if we take the belt from a 
dynamo and arrange for an equal current from some 
other source to flow through the armature in the same 
direction we must obtain motion, but in a direction 
opposite to that in which the armature was revolved 
when generating. 

Let us look at this a little more in detail. Figure 
55 shows the armature and fields of a motor. Cur- 

74 



Principles of Electric Motors — Direct Current 75 

rent is flowing into the armature through the brushes. 
We have seen that the two halves of such an armature 
are in parallel and that the current magnetizes the 
armature, setting up poles as indicated by N and S. 
Arranged as shown in the figure, the S pole of the 
laelds will attract the N pole of the armature and repel 
the S pole. This will cause the armature to move to 
the right and were it not for the commutator it would 
move only until the poles of armature and fields 
had aligned themselves. But as the armature moves 
the brushes change connections coil by coil and the 



.<^N 




Figure 55 



N and S poles of the armature remain always in th^i 
same position, thus keeping the armature always in 
motion in a vain endeavor to align itself and come to 
rest. Should we change direction of current either in 
field or armature, the motion would be in the opposite 
direction. If current through both fields and arma- 
ture is reversed motion will continue in the same di- 
rection. The pull of the armature is governed by the 
current flowing in it and the strength of the fields. 
Since the motor is the exact counterpart of a dy- 



76 Operating and Testing 

namo and its armature operates in a field precisely 
similar to that of a dynamo, it follows further that it 
must generate an E.M.F. just like a dynamo, and so 
it does, and this E.M.F. is always opposed to that of 
the dynamo from which the motor receives its cur- 
rent. This E.M.F. is known as the ''counter E.M.F.'' 
of the motor and varies with the strength of field and 
speed of armature, or, in short, with the rate of cut- 
ting lines of force just as the E.M.F. of the dynamo 
does. The current which flows from the dynamo to 
the motor varies as the difference between the E.M.F. 
of the dynamo and the counter E.M.F. of the motor. 
Thus, if the voltage of the djTiamo be 110 and the 
counter E.M.F. of the motor 105, the current flow 
through the motor will be due only to the five volts. 
The torque or pull of a shunt motor will depend upon 
the current, and consequently as a greater load comes 
on the motor, it must slow up until its counter E.M.F. 
is sufficiently reduced to allow^ the requisite current 
to flow. 

If the armature of a motor have a very high resist- 
ance, it follows that its counter E.LI.F. must be much 
lower than the E.M.F. of the dynamo in order that 
the necessary current may be forced through it. If 
with such an armature an additional load is thrown 
on, it must, of course, slack off in speed considerably 
in order to lower its counter E.M.F. sufficiently to 
draw the necessary current. The lower the resistance 
of the armature, therefore, the nearer constant the 
speed of the motor. This applies also to the resistance 
of the line. This fact is often made use of in regu- 
lating the speed of motors, an artificial, variable re- 



Principles of Electric Motors — Direct Current 77 



sistance, known as a rheostat being cut into the circuit 
to control the speed- 
So long as the motor is at rest, it has of course no 
counter E.M.F. If, at such a time the dynamo cur- 
rent were turned on, the armature of the motor would, 
up to the time that it acquired its proper speed and 
developed a counter E.M.F. , present a circuit of very 
low resistance and be subject to an enormous current 
flow, which would speedily cause it to burn out. To 
prevent this a rheostat is always cut into the arma- 



I 







1 



WMWJwmi^ 

Figure 56 

ture circuit. Figure 56 shows diagrammatically the 
circuits of a simple shunt motor. When the motor is 
to be started, the arm O of rheostat R is gradually 
moved, cutting out resistance. 

The speed of a motor can be made to vary, first, by 
adding resistance in the armature circuit. This we 
have seen will tend to slow it down. Second, by in- 
creasing the strength of the field it can also be made 
to run slower. With a stronger field not so much 
armature speed is necessary to develop a given counter 



78 Operating and Testing 

E.M.F. and as this can never exceed the B.M.F. of the 
dynamo it follows that the motor must slow up. Con- 
versely, by weakening the fields we can increase the 
speed of the motor, but if the fields are weakened too 
much, the armature may not be able to do the work 
and the counter E.M.F. fall so much below that of 
the dynamo that the armature will burn out. 

The effect of a wrong position of the brushes is 
evidently quite different with motors than with d}Tia- 
mos. Suppose the brushes, Figure 55, to be moved 14 
turn in the direction of motion. This will throw the 
N and S poles of the armature in perfect line with 
the polarity of the fields, and in this case the arm^ature 
would have to come to rest. There would be no coun- 
ter E.M.F. and the rush of current would burn up the 
armature wires. Again, suppose the brushes to be 
moved one-half revolution forward or backward, the 
direction of motion vriW be reversed. 

The magnetism of the N. pole of armature, of 
course, repels the magentism of the N. pole of the field 
just as it does in a d^Tiamo. Hence with an increase 
of current through the armature which always fol- 
lows increase of load, the neutral line is shifted in the 
opposite direction in which the armature revolves and, 
to avoid sparking, the brushes must be shifted just 
in the opposite Avay to those of the dynamo. The 
same considerations that apply to short circuiting coils 
in an active part of the field of a dynamo apply to 
motors. The position of least sparking at the brushes 
is not, however, the position of greatest torque. 
The greatest pull is obtained when the brushes are set 
somewhat back of the neutral. If the brushes are 



Principles of Electric Motors — Direct Current 79 

shifted in either direction far from the neutral line, 
some of the coils will not be generating any counter 
E.M.F just as in the dynamo, and, consequently, if the 
motor is running empty, it will speed up. If the mo- 
tor is loaded, the armature will not be able to pull the 
load and slow do^\TL and very likely burn up. 

The maximum speed of any motor is that at which 
its counter E.M.F. most nearly equals the E.M.F. of 
the circuit. This speed can be approximately at- 
tained when the motor is doing no work. 

The losses in the motor are due to the same causes 
as those in the dynamo. A certain amount is due to 
friction. There is a loss of potential due to the re- 
sistance of the line and a further loss due to the arma- 
ture resistance. This in the armature, if excessive, 
will manifest itself by much heating. 

If the fields are wound with a few turns of large 
wire instead of many turns of fine wire an unneces- 
sarily large current will be required for magnetiza- 
tion. If a poor quality of iron is used in the fields, 
or if the air gap between pole-pieces and armature is 
too great, the magnetic circuit will be of low conduc- 
tivity (see chapter on magnetism) and require un- 
necessary power to generate. 



CHAPTER YII 

TYPES OF MOTORS — DIRECT CURRENT 

There are as many different types of motors as 
there are of dynamos. Any dynamo may be used as a 
motor and any motor as a dynamo, as we have seen 
in another chapter. It is merely a question of apply- 
ing current properly. 

In the matter of regulation," however, there is con- 
siderable difference. AYe shall begin our study with 
the oldest and now almost obsolete form — the con- 
stant current series motor. This motor is made only 
in small units and used only on arc light circuits. 
The amperage of an arc light circuit does not usually 
exceed ten amperes. To obtain even 5 H. P. with 
ten amperes would require a voltage of about 400 
volts, hence it can readily be seen that such motors 
are not commercially practicable except in small 
units and then only when no constant potential cir- 
cuit is available. 

The torque or pull of any series motor, if the fields 
are not oversaturated, is proportional to the square 
of the current. Doubling the current doubles the 
strength of fields, and as the same current passes 
through the armature its strength is also doubled, 
hence the power of the couple is quadrupled. 

80 



Types of Electric Motors — Direct Current 81 

We have seen in a previous chapter that the speed 
limit of any motor armature is that speed at which 
the counter E.M.F. is equal to the E.M.F. existing at 
its terminals. These two can of course only be equal 
when no current is flowing, i. e., when the motor is 
doing no work. As we are here dealing with a cur- 
rent which is kept at a certain value by the dynamo, 
w^e need take no precautions to keep the current from 
damaging the motor. If now such a motor be started 
with a load it will at once develop its full torque or 
pulling power, the maximum current being instantly 
available in fields and armature. The torque will also 
be constant since field and armature are of constant 
resistance. The counter E.M.F. of the motor has no 
effect upon the circuit except to require the genera- 
tor to work at a higher pressure. The speed of such 
a motor will vary as the load put upon it. If the load 
be removed from such a motor it will increase its speed 
and oppose the dynamo E.M.F. ; this in turn will be 
increased and again the motor speed will be increased 
in a vain endeavor to build up an E.M.F. equal to 
that of the dynamo. If this racing of the motor is 
not checked by an increase of load or a regulator of 
some kind it will continue to speed up until it flies 
to pieces. The speed regulation of this motor is 
usually accomplished by reducing the field strength 
as the load decreases and increasing it as the load in- 
creases. The methods employed are similar to those 
illustrated in Figures 40 and 41. 

We may next consider a similar motor on a constant 
potential circuit. The torque in this case is propor- 
tional to the square of the current as above. But in 



82 



Operating and Testing 



this case the generator is without control over the 
current. If current is turned on suddenly before the 
armature is in motion there is only the ohmic resist- 
ance of the line, fields and armature to prevent it from 
rising to an enormous value. In well designed instal- 
lations these are all low and the result would be a 
burned out armature. Hence the resistance R, Figure 
57, is provided. This motor loaded down will act as has 
been described under Principle of Motors, the arma- 




WNWW 



Figure 57 

ture tending to run at a speed at which it develops a 
counter E.M.F. equal to the E.iM.F. existing at its 
terminals. With a heavy load the motor must slow 
down considerably to permit the necessary current for 
doing the work to pass. " As the load is removed the 
current flowing becomes less because the motor speeds 
up and the counter E.M.F. begins to rise. This in 
turn weakens the fields Weakening of the fields les- 
sens the counter E.M.F. of the motor and consequently 



Types of Electric Motors — Direct Current 83 

it speeds up to make up for this. As the motor speeds 
up more and more the fields become gradually weaker 
and weaker, thus calling for still more speed in an 
endeavor to bring the counter E.M.F. up to the initial 
E.M.F. of the chiiamo. This speeding up of a series 
motor without load will continue until the armature 
flies to pieces. For this reason such motors are as a 
rule used only where an attendant can be kept con- 
stantly with them. 

As a rule this motor is used only in street railway 
work and on cranes, etc. In this case an attendant is 
necessary anyway. The motor because of its great 
starting power is best suited for this work, and any 
other kind of motor would moreover be entirely un- 
suitable, because very often the current is suddenly 
stopped or put on because of the trolley wheel leaving 
the trolley. AVith this type of motor there can be 
no current through the armature unless there is the 
same current through the fields. Consequently every 
rush of current (the armature being in motion, as it 
always is when the w^heel for an instant leaves the 
trolley) is met by the proper counter E.M.F. , which 
prevents undue current flow, and there is no need 
of regulation unless the speed of the armature has 
been much reduced during the time current flow was 
interrupted. 

The motor most in use for general work is known 
as the shunt motor. The fields and armature of this 
motor are entirely independent of each other. In 
operating this motor it is necessary to see that full 
current is in the fields before any current is allowed 
to pass into the armature. The armature current 



84 Operating and Testing 

must then be turned on gradually so as to give the 
armature time to get in motion and develop the neces- 
sary counter E.M.F. before the full current is turned 
on. This is accomplished by means of the rheostat 
R shown in Figure 56. The speed of this motor is 
nearly constant under variable load within proper 
limits if it has been well designed and installed with 
low resistance in armature and line. It cannot be 
used in connection with street car work, principally 
on account of the inductance of its fields. The fields 
of a shunt motor always contain a great many turns 
of wire, and it requires some time for the current to 
attain its full value in them. If the current were cut 
off from such a motor for, say, a second and then ap- 
plied again, as often happens in connection with trol- 
ley service, the fields w^ould in that second have lost 
their magnetism and upon the connection being re- 
established the motor would be running without fields 
and, of course, without its proper counter E.M.F. 
This would invite a very strong flow of current 
through the armature before the fields have time to 
build up, and furthermore a good armature without 
counter E.M.F. would offer almost no resistance and 
be equivalent to a short circuit and this w^ould entirely 
prevent the fields from getting current so that either 
a fuse or circuit breaker would go out or the armature 
would burn out. To prevent accidents of this kind 
rheostats with overload and underload switches have 
been devised which entirely disconnect the motor if 
the current fails. 

The compoimd motor varies from the shunt motor 
just as the compound dyanmo does from the shunt 



Types of Electnc Motors— Direct Current 85 

dynamo. A compound wound motor may, however, 
be used in two ways. If the current in the series 
winding is in the same direction as that in the shunt 
winding the fields will be strengthened as the load is 
increased. This will enable the armature to develop 
its counter E.M.F. ^rith a lesser number of revolu- 
tions and therefore it will slow up. The power of a 
compound motor so connected will increase as the 
load is increased but the speed will decrease. 

If the current in the series fields flows in the oppo- 
site direction to that in the shunt fields the magnet- 
ism in the fields will be lessened as the load increases. 
This will force the armature to move at a higher rate 
of speed in order to develop an E.il.F. equal to the 
E.M.F. at its terminals. If the series fields are prop- 
erly proportioned to the shunt fields and the resist- 
ance of armature and line, the motor will run at a 
uniform speed with any load within its capacity. It 
will be noted, however, that the current through the 
armature with such a motor increases as the load in- 
creases much more rapidly than with an ordinary mo- 
tor since it must make up for the deficiency created 
in the fields by the opposing magnetism. The capac- 
ity of two identical motors, one shunt wound and the 
other ^^differential," as this winding is termed, is 
therefore not equal, the differential motor having a 
much smaller capacity. 

As the differential motor uses power to neutralize 
power, i. e., the current in the series fields acts against 
that in the shunt fields, its efficiency is lower than that 
of any other direct current motor and its use in gen- 
eral is not to be recommended except where great 
constancy of speed is absolutely necessary. 



CHAPTER VIII 

PRINCIPLES OF ALTERNATING CURRENT MOTORS 

Many of the types of small direct current motors 
may be run on alternating current circuits. That this 
is true is readily apparent when it is recalled that 
changing the direction of flow of current in a direct 
current motor (both fields and armature) does not 
reverse its direction of rotation. When current flows 
through the motor in a positive direction, for instance, 
there is a certain attraction between those poles set 
up by the field current and those poles set up by the 
armature winding. If the direction of flow of cur- 
rent is reversed each of these sets of poles is reversed 
and the same attraction exists as before. 

Every coil of wire wound on an iron core, as in the 
case of a field magnet, has a certain inductance, which, 
v\^hen an alternating current is sent through it, acts 
as a resistance and tends to cut do\\Ti the current 
flow. It is due to this fact that the majority of di- 
rect current motors, especially the larger sizes, can- 
not be used on alternating current circuits. If a di- 
rect current motor were constructed without iron 
either in the fields or armature it would operate on 
alternating current as well as on direct current. This 
characteristic is taken advantage of in some form^j of 

86 



Principles of Alternating Current Motors 87 

integrating watt-meters which are suitable for use on 
either direct or alternating current circuits. 

If two identical alternating current generators were 
run, one as a generator supplying current to the other 
as a motor, the one running as a motor would run in 
exact synchronism and at exactly the same speed as 
the one running as a generator, for every change in 
the force producing power in the generator would be 
reproduced in the motor. This can be more readily 
understood by a study of the effects in a simple case. 
Suppose two bi-polar machines each have an arma- 
ture consisting of a simple loop the ends of which are 




Figure 58 

connected to two collector rings, as shown in Figure 
58. The fields of both the generator and the motor 
must be supplied by direct current from some outside 
source. If the armature of the generator G is re- 
volved to the right, as indicated by the arrow, current 
would be induced in the moving coil in the direction 
shown by the other arrow. This current flowing in 
the coil of the motor M would set up poles, as indi- 
cated by the dotted line S N, and these poles would 
be acted upon by the polarity of the fields, which is 
permanent, as shown. A north pole N will attract a 
south pole S and repel another north pole. This re- 



88 



Operating and Tesiutg 



suits in motion and the armature of the motor is re- 
volved toward the left. 

The successive steps for a half revolution are illus- 
trated by the figures in Figure 59, where the figure 
at the left represents the various positions of the gen- 
erator coil, 1, 2, 3, 4, 1', as it makes a half revolution. 
The several figures at the right show the resulting 
condition and corresponding position assumed by 
the motor armature. 1 represents the position of the 
armature, as shoA^n in Figure 58. At this point the 
generator coil is generating its maximum current. 
This current flowing through the coil of the motor 








V 



Figure 59 ^ 

produces a field of force with a polarity, as shown in 
the head of the arrow, indicating an N pole, and as 
the generator armature is requiring at this point the 
greatest expenditure of energy to turn it so is the 
motor armature yielding its greatest turning effort. 

When the generator armature has revolved to point 
2 the conditions in the motor armature are as shown 
in 2. There is the same tendency to turn the motor 
armature as before, but as the current in' the genera- 
tor armature is decreasing so is the tendency to turn 
in the motor armature likewise decreasing As point 3 
is passed the direction of the current produced by 



Principles of Alternating Current Motors 89 

the generator armature is reversed and also the po- 
larity of the motor armature, and at point 4 the con- 
ditions in the motor armature are as shown at 4. It 
will be noticed that the current in the motor arma- 
ture is now flowing in the opposite direction, with the 
result that the relation between the armature and 
field polarities are repeated, and the motor armature 
will continue to revolve in synchronism with and at 
exactly the same speed as the generator armature. 

If the single coil generator just described is in op- 
eration and connection made to the motor armature 
while this armature is at rest, it will be quite evident 
that the motor armature will not revolve, for, w^hen it 
assumes the position shown in 3, Figure 59, it will be 
on a dead center and there will be absolutely no turn- 
ing moment. 

In order that the motor armature may continue to 
revolve it must have acquired some momentum to 
carry it over the dead center and it must also move at 
such a speed that it will always be at or near the dead 
centers when the dynamo current reverses. If it is 
not its m.ovement will be opposed by the reaction be- 
tween the poles of its armature and fields and come 
to rest. For this reason it is necessary to bring single- 
phase synchronous motors up to synchronous speed 
by some outside means before connecting it to the sup- 
ply current. 

Some polyphase s>Tichronous motors are so designed 
that they will bring themselves up to speed if started 
under no load. 

Owing to the fact that synchronous motors are not 
self starting and that some outside means must be 



90 Operating and Testing 

employed to bring them up to synchronous speed and 
due to the further necessity of a direct current field 
excitation they are seldom used for ordinary com- 
mercial work, their use being confined to large imits 
in such places where they can be used under the above 
conditions. 

If the field excitation of a synchronous motor is 
varied the power factor is also altered and it is possi- 
ble by varying the exciting current to produce a 
leading ''current/' this causing the motor to have 
the same effect on the line current as would be caused 
by the introduction of a condenser. This character- 
istic is sometimes taken advantage of to increase the 
power factor on lines where it is low. 

For the ordinary purposes for which motors are 
used neither of the motors just described is suitable. 
To be commercially practical a motor must be self 
starting and must be capable of starting under a load. 
It must require current from one source only, i. e., 
must be self-exciting. The ''induction" motor ful- 
fills these requirements, and is the form of motor in 
most common use on alternating current circuits. 

The principles underlying the operation of a poly- 
phase induction motor can be gathered from a study 
of Figure 60. In this figure the heavy black lined 
circles represent the wires of one phase, A, and the 
light those of the other, B, of a two-phase motor. 
These windings are placed in the slots of the stator as 
shown at the top of the figure and the small circle 
represents one of the bars of a squirrel cage arma- 
ture, as shown in Figure 62. This circle also marks 
in the different sections of the drawing 1, 2, 3, etc. 



Principles of Alternating Current Motors 91 




Figure 60 



the position of a steadily advancing pole, in this case 
a north pole. 

The wires A and B are traversed by two independ- 



92 



Operating and Testing 



ent alternating currents which are, however, always 
in the phase relation illustrated in Figure 61 and in- 
dicated as to direction by a cross for positive and a 
dot for negative. In Figure 61 that portion of the 
currents represented by the sine curves above the 
base line may be taken as positive and those below it 
as negative. 

To begin let us assume that the current in A is at 
a maximum, as showTL under 1 in Figure 61 ; at the 
same instant the current in B is zero; under these 
conditions B will not be producing any lines of force 



A 


1/ 


1 


/ 
/ 








5 i 


* - 


7 i 

1 




/ 

/ 
/ 
/ 
/ 


\ 


B 










\ 


V 


\ 


I 


y 


1 
1 

f 







Figure 61 

and A will be producing a magnetic field, as shown in 
1 in Figure 60, the lines of force encircling the wire 
in which the current is positive (flowing away from 
the observer) in the direction in which the hands 
of a clock move. This produces a north pole at the 
wire C. A moment later the two currents assume the 
phase relation shown under 2, Figure 61, and the 
field becomes now as indicated at 2, Figure 60. The 
currents in both sets of wires now being in the same 
direction the lines of force expand and encircle both 
of them and the north pole is moved further to the 



Principles of Alternating Current Motors 93 

right. In another short interval A sinks to zero and 
B arrives at its maximum, as shown under 3, Figure 
61. This in turn produces the field conditions, as 
shown at 3, Figure 60. As the two currents continue 
to rise and fall always maintaining the same phase 
relation (90 degrees apart), the field continues to 
change with them, as shown further in 4 and 5. 

It will be noticed that all of the poles set up by the 
different convolutions are moving steadily from left 
to right, and it can also be seen that if we should re- 
verse the two phases the poles would shift in the 
opposite direction. 

If, while this shifting of poles is going on, the 
wire C should remain stationary it would cut the lines 
of force rapidly moving by it just as it w^ould in any 
dynamo in w^hich the lines of force were stationary 
and the wire moving. In this way currents would be 
induced in it. These currents w^ould be in such a 
direction that the lines of force created by them w^ould 
oppose the lines of force creating them. This oppo- 
sition betAveen the wire C and the field would result 
in motion if C were free to move. If C were to move 
at the same rate of speed as the revolving field it 
would cut no lines of force and no currents would be 
induced in it. It can in practice never move at this 
speed because it would then have no torque. 

It can be seen from the above that the difference in 
speed between the revolving field and the Viive C, or 
of an armature carrying many wires like C, must 
depend upon the load, and the greater the load the 
greater must be the difference in speed between the 
tAvo. In other words, in order to carry a heavy load 



94: Operating and Testing 

such an armature must slack up in speed sufficient to 
allow of induction enough so that the reaction be- 
tween the two currents may be sufficient to move the 
load. This difference in speed is spoken of as the 
'^slip.'' If the load is too heavy the motor will sim- 
ply come to rest and burn out. 

It can also be seen that, if instead of a squirrel cage 
armature or rotor we provide one with a regular ar- 
mature winding the induced currents can be brought 
outside of the machine and be controlled by resist- 




Figure 62 

anee like those of any dynamo or motor armature. 
This is often made use of in large motors. 

The rotor of an induction motor acts like the sec- 
ondary of a transformer and if it is at rest while cur- 
rents are traversing the stator, the effect is the same 
as though a transformer were short circuited. For 
this reason these motors require enormous starting 
current for a short time, sometimes five or six times 
the running current. 

In Figure 62 is shown the armature of an induction 
motor. The armature consists of a laminated iron 



Principles of Alternating Current Motors 95 

core with partially closed slots through the outer 
edge. Insulated copper bars inserted in these slots 
are bolted to rings on each end of the armature and 
are thus short circuited. This is called the ^^ squirrel 
cage'^ type of armature owing to its similarity to the 
ordinary squirrel cage. The field is also formed of 
laminated iron cores with slots across its face into 
which the field windings are placed. 

In some designs of induction motors the element 
which has here been called the ^ Afield" is made the 
revolving element, the *^ armature" winding being 
placed on the stationary part of the machine. The 
conditions, so far as the operation is concerned, re- 
main the same whether the armature or field revolves 
but certain peculiarities in the design of the larger 
size motors, especially, make it preferable to have the 
field revolve. 

The two terms ^^ armature'' and 'Afield" have a 
rather indefinite meaning when applied- to alternate 
current motors. The field is generally considered as 
that element which receives current from the line 
w^hile the armature is that part in which current is 
induced. The more common term applied to these 
parts is ^^ rotor" for the revolving element and 
^^stator" for the stationary element, although owing 
to their similarity with a transformer the field is 
sometimes called the primary element and the arma- 
ture the secondary element. 



CHAPTER IX 



TYPES OF MOTORS ALTERNATING CURRENT 



Single phase motors may be made self starting in a 
manner illustrated in Figure 63. This figure shows 
a diagram of the connections of a split phase motor. 
There are two sets of field windings and each has a 
different reactance, that is to say, one will permit a 
more rapid rise of current strength than the other. 




Figure 63 

This a(3tion is as follows. The two semicircles in the 
center of Figure 63 surround the armature shaft. 
There is also a circular piece which revolves with the 
armature and whidi normally while at rest closes the 
circuit through the fine wire winding at the center. 
"When current is turned on there is a flow through tho 

96 



Types of Motors — Alternating Current 97 



heavy winding and also through the fine, but there 
is considerable difference in phase between these cur- 
rents and they set up a field, as already explained, for 
two phase motors. This causes the motor to start as 
a two phase motor and when it has attained its proper 
speed the circuit through the semicircle is opened by 
centrifugal force which causes the outer ring to spread 
out. The motor now runs as a single phase induction 
motor. 




Figure 64 

Another form of motor is shown in Figure 64. The 
armature contains a direct as well as alternating cur- 
rent winding. The motor is started by throwing the 
switch S (blades not shown) to the left. This sends an 
alternating current through the fields and armature 
and starts the motor. After it has come to speed the 
switch is thrown to the right ; this sends the current 
through the alternating current side of the armature 
and also closes the direct current side through shunt 
fields and rheostat (the switch closes the connections 



98 



Operating and Testing 



at 1 and 2). The motor now is synchronous with 
separately excited fields, the field excitation being fur- 
nished by the D. C. side of the armature. 

The three phase motors up to a capacity of 5 H. P. 
are not usually equipped with starting devices. Such 
motors are self starting but require enormous cur- 
rents w^hen starting with load. Sometimes these cur- 
rents are 5 or 6 times the running current. In order 
to allow such currents to be used at starting and still 
have adequate fuse protection when running the 
method shown in Figure 65 is generally employed. The 




Figure 65 



switch is thrown up to start and the current does not 
pass through the fuses. After the motor is running at 
its normal speed the switch is thrown downward, 
thus forcing the current to pass through the fuses 
and protecting the motor As an extra safeguard the 
switch in its first position is sometimes forced against a 
spring which would throw it out of connection if left 
there, thus assuring that the attendant will remain 
with it until the motor is running so he can throw 
it to the running position. 



Types of Motors — Alternating Current 99 



Polyphase motors are essentially constant speed 
motors. Any regulation of their speed is quite un- 
economical. They are all self starting and all subject 
to the same heavy rush of current at starting, as noted 




Figure 66 

above. In the smaller sizes only the stator carries 
windings unless for some special reason the rotor is 
also wound. The general appearance of the stator 




winding is shown in Figure 66. This is a 3-phase 
winding and the windings interlace all the way 
around. Diagrammatically such windings are usually 
represented as in Figure 67. 



100 



Operating and Testing 



The windings of the three phases are shown in 
Figure 67. If we connect adjacent ends together we 
shall have what is known as the delta or mesh winding. 
If instead we connect the ends 1, 2, 3 together, we ob- 




Figure 68 

tain the Y or star winding If a motor connected up in 
Y be changed to delta it will require much more cur- 
rent. If connected from delta to Y it will require less 
current. Of course, in both cases the heating will 




Figure 69 

change with changes in the currents used, so that the 
change in connections must not be recklessly made. 

There are two methods of starting induction mo- 
tors in general use. On.e of these consists in inserting 



Types of Motors — Alteyniating Current 101 

resistances in the rotor circuit, as illustrated in Figure 
68, at R. This is commonly used only with the larger 
motors. This resistance may be so proportioned that 
the starting power of the motor will be just as great 
with it in circuit as without it, and where great start- 
ing power is necessary this is a ve-ry useful method. 

For the smaller and cheaper motors above 5 K. P., 
the method shown in Figure 69 is mostly used. While 
the switch is in the position shown the current must 
pass through the auto transformer R. The amount of 
reactance can be adjusted by connecting the wires, 1, 
2, 3, at different points on R. The more reactance 
there is placed in the circuit the slower will be the 
starting of the motor. When the motor has attamed 
sufficient speed the switch is thrown up and the cur- 
rent at full voltage goes direct into the motor. 



CHAPTER X 

DYNAMO OPERATION — DIRECT CURRENT 

The dynamo room should be so situated that it is 
not exposed to moisture or the flyings of dirt and 
combustible material. There is nothing that will help 
induce an engineer to keep appliances in good work- 
ing order more than a well ventilated and lighted 
room. 

The larger dynamos are now generally direct con- 
nected, and should be placed upon foundations en- 
tirely separate from those of the building. This pre- 
caution is due principally to the vibrations caused by 
the engine. Where dynamos are belt driven there is 
very little vibration, unless the machine is entirely too 
heavy for the flooring upon which it is placed. 

Whatever the power may be, whether steam, water, 
gas or gasolene, it is of the utmost importance to see 
that the prime mover operates as steadily as possiWe. 
The slightest fluctuation in speed will show in con- 
nection with incandescent lights. For this reason it is 
preferable to have the engines used for the lighting 
entirely separate from all other work that may be 
going on. This, of course, does not apply to factories, 
where only an indifferent light is required, as much as 
for central stations, where power is being sold. 

102 



Dynamo Operation — Direct Current 103 

If belt driving is necessary the machinery should 
be arranged that the belting may run as near hori- 
zontal as possible and the direction of rotation should 




Fimire 70 



be such that the belt will pull on the under side. This 
allows the slack of the belt to hang downward on the 




Figure 71 



upper side and increases the arc of contact, as illus- 
trated in Figure 70, whereas a belt operating as that 




Figure 72 

sho^ra in Figure 71, by its slack decreases its arc of 
contact with the pulleys. Whenever it is necessary to 
arrange belting as in Fignre 72, it becomes necessary 



104 



Operating and TesUng 



to keep the belts very tight. This is apt to result in 
hot bearings and also increases the amount of power 
necessary to operate. 

It is best to choose belting that is considerably heav- 
ier than would be absolutely necessary to do the work. 
In order to obtain a certain amount of work from a 
belt there must be a certain pressure exerted by the 
belt upon the pulleys. This can be obtained by 
stretching a small belt very tight, but is far better 
obtained with a much larger belt operating with con- 




Figure 73 

siderable slack. Such a belt will last much longer 
and will need very little attention, while the smaller 
will need continually to be tightened. The smoothest 
side of the belt should be run next to the pulley, as it 
makes the most perfect contact. The face of the pul- 
ley should be smooth, as all roughness tends to wear 
the belt and does not add a bit to the adhesion. "Wher- 
ever practicable it is best to have belts made up end- 
less; especially where the speed is quite high. "With 
slow speed belting the lacing will not cause much an- 
noyance, if it is well done. 



Dynamo Operation — Direct Current 105 

A good method of lacing is shown in Figure 73. 
The holes should be made rather oblong, as shown, as 
in this way we avoid cutting away so much leather. 
On no account should any laces be run crosswise of 
the belt on the side next to the pulley. 

In placing belts it is always best to put the belt 
upon the smaller pulley first. Never allow oil to 
come in contact with rubber belting. Use only tallow 
or castor oil on leather belting. Grease can be re- 
moved from leather belts by the use of turpentine. 

The generator or motor should always be provided 
with a sliding frame, so that it can be adjusted to suit 
the belt from time to time. If the belt is properly ar- 
ranged, there will be some lateral play possible at the 
generator shaft; this is essential to smooth running 
and helps to secure even distribution of the lubrica- 
tion. 

The tension on all belts that are run tight should 
be relieved when the belt is not in use. 

Double belts should not be used on pulleys of less 
than three feet diameter. 

The proportion between two pulleys close together 
should not be greater than 6 to 1. 

If one is limited to a certain width of belt the power 
can be increased by increasing the diameter of both 
pulleys in the same ratio. This will not affect the 
speed of the machinery, but will increase the speed of 
the belt and hence its power in the same ratio that 
the speed is increased. 

The width of a single belt can be found from the 
following formula: 

W = 1200 X H.P. -f- V 



106 Operating and Testing 

where W is the width of the belt in inches and V the 
velocity of belt in feet per minute. For double belts, 
use 800 instead of 1200. This formula will give belts 
of ample size and, if necessary, much smaller belts 
can be forced to do the work. 

STARTING-ARC DYNAMO 

Before attempting to start the dynamo the circuit 
should be tested out to see that it is complete. If this 
is found in order, the belts should be examined f'or 
tightness ; the bearings should be well oiled ; all iron 
tools, etc., should be removed from proximity to the 
machine lest they be attracted. by the magnetism that 
will be developed and cause injury It will also be 
well for the operator to leave his watch, unless it is 
shielded against magnetism, as far as convenient from 
the d^Tiamo. ]\Iany watches are brought to complete 
standstill by being brought too close to the fields of a 
powerful dynamo. 

These things all being in order, the dynamo may 
now be set in motion, and it should now be so shifted 
on the sides that the armature has considerable lat- 
eral play. This indicates that the belt is in proper 
position and also helps to distribute the oil and keep 
the bearings cool. 

If the machine operates at very high voltage, an in- 
sulated wooden platform should surround it on all 
sides, and this platform should be so placed and of 
such dimensions that no one can touch the machine 
without standing upon this platform This platform 
will be of no use unless it is kept perfectly dry, and 
to assist to this end should be well filled with shellac. 



Dynamo Operation— Direct Current 107 

It will also be well for the operator, especially if he 
be a novice, to provide himsef with rubber gloves, and 
these also to be effective must be kept dry inside and 
out. As a further precaution, the operator should 
make it a rule while working on pressures above 220 
volts, to touch bare metal parts with one hand at a 
time only. If this precaution is observed and if the 
body is kept well insulated from the ground there will 
be but little or no trouble experienced from shocks. 

If the frame of the machine is grounded it will help 
to make things safer for the attendant, but will place 
a greater strain on the insulation. It will then be 
impossible for any one to obtain a shock by coming in 
contact with the frame, but greater care must then be 
exercised to avoid touching bare live parts and the 
frame at the same time. 

Under no circumstances must one over touch liigh 
potential wires while standing upon wet ground, 
boards, cement, metal connected to earth or upon any- 
thing that is not known to be a good insulator. 

The regulator should now be examined to see that 
it is in proper working order and runs smoothly. Next 
place the brushes in position so that they bear prop- 
erly upon the commutator. Before doing so, note that 
the armature is running in the direction called for by 
the position of the brushes. If it is not, one or the 
other must be changed about. 

The plugs may now be inserted into the proper holes 
on the board. If there is sufficient residual magnet- 
ism in the fields the machine will begin to generate 
and, by noting the ammeter, the rise in current can be 
observed. If the residual magnetism is weak or en- 



108 Operating and Testing 

tirely absent, as sometimes occurs in new machines, 
or such as have been idle for a long time, it may not 
build up with all of the lights in the circuit. In such a 
case it is best to start the machine with one or two 
lights in circuit and when the current has attained to 
its full value to open the circuit and force current 
through the other lamps. 

If there is no residual magnetism whatever, even 
this expedient will not suffice to start generation and 
current from some outside source, either from another 
generator or from a battery, must be caused to flow 
around the fields. Only a very small amount of cur- 
rent is required for this purpose. 

It is most important, however, that the current from 
such a battery flow around the fields in the same di- 
rection as the current from the armaure would flow. 
If this is wrong in the first trial, it is but necessary to 
reverse the battery connections. Sometimes a machine 
can be started generating by striking the metal of the 
fields with a hammer in a gentle way. 

When the machine is fully staited, the next point 
of importance is to see that the polarity is correct. 
Unless the current enters the arc lamps at the proper 
terminal, the lower carbon will be consumed at the 
fastest rate and will, in a short time, burn down to 
the carbon holders, which will in turn be speedily de- 
stroyed. If the polarity of the machine is wrong, it 
can be corrected by changing plugs, as explained un- 
der switching, or the polarity of the fields be reversed, 
or the leads to the armature changed, as indicated, 
in chapter on current generation. 

Other methods of determining the polarity are given 



Dynamo Operation — Direct Current 109 



elsewhere, but the omIv one generally used in a case 
like this is that of observing the arc lamps. The pos- 
itive carbon will heat to a greater extent than the 
negative and consequently will remain warm longer 
and also, if the lamp is burning right, the brightest 
light will be thrown downward, while if the other 
way a bright light and strong shadows will be thrown 
against the ceiling. 

If there are more lights on a circuit than one ma- 
chine can handle, two may be connected in series as 
shown in Figure 74. In such a case the regulator of 



+ 




mm 



s 



Jo 

11 



Figure 74 

one machine is generally cut out and the brushes set 
for the highest potential at which this machine will 
operate well. The regulator on the extra machine is 
then depended upon to take care of the variations in 
the number of lamps cut into the circuit. 

An expedient sometimes resorted to when a number 
of circuits are run from one machine as illustrated in 
Figure 75 and when there is an open circuit in one of 
them, is to cut out the bad line for a time by the plugs 
indicated by dotted lines at P, until the lights in the 
other circuit are burning full, then suddenly with- 



110 



Opei^ating and Testing 



draw the plug. This throws the whole accumulated 
force of the machine into the bad line, and if there is 
any possibility whatever the current will jump the 
bad place and often times operate the circuit success- 
fully thereafter. This practice is known as ''jumping 
in," and should ^ever be resorted to when any other 
method is available, as it may ruin the dynamo or 
cause fire or a breakdown of the insulation somewhere 
along the line. 

\L \U \U \l/ 

Z t t (D 
t t 0) (0 

$ 9< $ >i< 

9 ql^ 9 






Figure 75 

To shut down the dynamo we close the switch shown 
at S, Figure 74. This shunts the current around the 
fields, and leaves them wtihout magnetism, thus caus- 
ing the current to sink to zero. On no account except 
that of extreme emergency must a series circuit oper- 
ating at high potential be broken suddenly. Such an 
interruption causes an enormous rise of potential for a 
very brief interval, which very often breaks down the 
insulation of the machine. The arc which follows the 
plug when it is suddenly withdrawn, is also often dan- 



Dynamo Operation — Direct Current 111 



gerous to the operator. If, however, such a circuit 
must be opened it should be done with a rapid motion 
and the operator should station himself so that the end 
of the plug or wire cannot strike him. 



STARTING SPIUNT DYNAMO 



In latter day practice it is very seldom that a shunt 
dynamo is used with variable potential or constant 




Figure 76 

current systems. Such machines are limited to con- 
stant potential w<Drk and variable currents. The con- 
nections of a shunt dynamo and switchboard are 
shown in Figure 76. The same general considerations 
that apply to arc machines also apply here. 



112 Operating and Testing 

To start the generation, we first disconnect the ma- 
chine entirely from the circuit. This is not always 
necessary, as many machines will build up success- 
fully with the whole load connected. Nevertheless, 
however, it is safer to disconnect the load. When 
the machine has been set in motion, we observe the 
voltmeter and by means of the rheostat R regulate 
the current through the fields, so that the voltage 
gradually approaches its proper value and remains 
stationary. When this point has been reached the 
main switch can be closed and the lights will burn. 

Unlike the series arc machine the shunt machine 
can do nothing while there is a short circuit on the 
line. There being no regulator the current immedi- 
ately rises to its highest possible value and the pres- 
sure of the dynamo sinks to zero approximately. This 
machine cannot be started while it is connected to a 
short circuit, because all of the current generated will 
flow through this ^^short," which acts as a shunt to 
the fields. The ^^ short" coming on while the machine 
is working wlil cause a momentary rise in current 
strength; it will also act as a shunt to the fields and 
deprive them of all current, thus finally reducing the 
E.M.F. of the machine until no more current is gener- 
ated If the armature is wound so as to stand this 
current for a fraction of a second, it will do no harm 
to the dynamo. 

In large installations it is customary to operate a 
number of dynamos in parallel. During the day, 
when the load is light, it will be taken care of by one 
of the dynamos and as the load increases more ma- 
chines will be connected to the board to help out the 



Dynamo Operation — Direct Current 113 

first one. If we have nothing but plain shunt ma- 
chines, it is not advisable to attempt operation in par- 
allel. It is practically impossible to keep two shunt 
machines at the same potential, and the one having 
the higher voltage will take the greater part of the 
load and also, when the difference amounts to as much 
as a few volts, run the other as a motor. This acci- 
dent occurs frequently, and generally with so little 
disturbance that the attendants know nothing about 
it unless they happen to observe the belting or am- 
meters. 

When a number of plain shunt machines are to 
work on the same installation, it is best to divide the 
system and give each machine a share of it. If this 
cannot be done, the voltage of the two machines must 
be constantly watched and adjusted by means of the 
rheostat. 

For operation in parallel it is customary to provide 
compound d^Tiamos. The arrangement of the wiring 
on such machines is such that when one machine takes 
more than its share of current it strengthens the fields 
of the other and thereby causes the potential of the 
other to rise until it draws its share of current. Com- 
pound machines when properly designed and driven 
by good engines, can be operated together with perfect 
freedom, no matter what the difference in capacity of 
the machines may be. 

The connection and operation of two or more com- 
pound machines can best be understood if we refer to 
Figure 77, which shows the machine and switchboard 
connections of two such machines. It is essential to 
see that the ammeters A arie cut in, as shown in the 



114 



Operating and Testing 



diagram. If they are cut into the same side as the 
compound winding, the indications will be very unre- 
liable, since the current from this side of the machine 
lias two paths through which it may flow to the board ; 
one through the fields of the other machine and one 
through the main of its own dynamo. The equalizer 




niftififi 



iiiiill 



Figure 77 

wire E should be of ample size, the lower the resist- 
ance of this wn're the closer will be the regulation of 
the two machines. The main switches of the dynamos 
should be so arranged that the equalizer will be con- 
nected slightly before the other two wires are and on 
BO accoimt later. In order that such dynamos may 
work at their best, they should be run at exactly the 



Dynamo Operation — Direct Current 115 

proper speed. If this is not the ease, the relation be- 
tween the shunt and compound winding will be dis- 
turbed. If, for instance, the machine is run above it^^ 
intended speed, the magnetization of the fields will 
have to be below the usual point of saturation, and in 
this case the magnetization due to the series current 
will be greater than it should be and the rise in volt- 
age higher than intended. If, on the other hand, the 
speed is much below normal, more resistance will have 
to be cut out of the field circuit, and thus the fields 
may be saturated by the shunt winding alone, so that 
the series current will have far less effect than it was 
intended to have, and the rise in voltage as the load 
increases will not be sufficient. 

Many machines are provided with resistances placed 
in parallel with the series fields, and by means of 
these the series fields can be strengthened or weakened 
and in a measure adjusted to make up for variations 
in speed if they are unavoidable. The location of 
such resistances is indicated at C. 

It \\dll be well also to observe whether the series 
current circulates around the fields in the same direc- 
tion as that in the shunt winding. If it does not, the 
series winding will have the opposite effect of that 
intended, and there will be trouble and sparking at 
Mie brushes and a large falling off in pressure as the 
load is increased. 

To start a plant of compound dynamos we begin 
with a single machine. "When this has been brought 
up to speed and is running smoothly, we close the cir- 
cuit through the fields by means of the rheostat R and 
adjust this resistance until the dynamo gives the re- 



116 Operating and Testing 

quired voltage. It is better always to see that E is 
high at the start and gradually cut resistance out of it 
than to start with the resistance in R low. After the 
voltage is about up to its normal, we close the main 
switch. This, if there are many lights or motors us- 
ing current, will result in a modification of the pres- 
sure and we must again adjust R until finally it comes 
to a steady value at what it should be. 

If a load heavier than one machine can carry is 
likely to be found at the start, some of it had best be 
disconnected or circuit breaker or fuses may go out 
and cause delay. 

After the first machine is . started the second is 
brought up to speed in the same way and the voltage 
brought up as near as possible to that of the first ma- 
chine when the main switch may also be throwTi in. 
When this is done, it will be necessary for the attend- 
ant to observe the ammeters of both machines care- 
fully and quickly adjust the rheostats so that each 
machine will receive its proper share of the current. 
It must be borne in mind that the machine with the 
higher voltage will take the greater part of the load, 
and if sufficient diflPerence of potential develops be- 
tween them it will run the other as a motor. 

Before a newly set up machine is thrown in with 
another, it should be tested for polarity. In order 
that they may operate properly, similar poles of all 
machines must connect to the same bus bars. Two 
simple methods of testing for polarity are illustrated 
in Figure 78. At the left two lamps of the voltage of 
the machines are connected between the dynamos to 
be started and the bus bars, as shown. When the dy- 



Dynamo Operation— Direct Current 117 

namo to be thro^^n in is up to voltage, the pressures of 
the bus bars and this dynamo must balance, and there 
can be no noticeable current flowing through the 
lamps. If, however, the polarity of the new djTiamo 
is different from that of the others, the voltage of the 
system will be double that of one dynamo and the 
lamps w^ill burn at full candle power. If the lamps 



-/.^«. 



i 




Figure 78 

are dark, the polarities of the dynamos are correct for 
parallel operation. 

In lieu of the lamps the test can be made by insert- 
ing one wire from each pole of the d^Tiamo into a cup 
of water and noting the bubbles that form. If the 
polarity is correct the bubbles will form at the same 
pole of the switch on both machines. To a-void making 



118 



Operating and Testing 



short circuits with this, test, the bare ends of the two 
wires may be wrapped about a piece of wood about 
an inch long and the whole immersed in the water. 
Connect the same wires, one at a time, to the same 
poles of both switches and see that the bubbles come 
from the same wire. 

A switch board arrangement often used with either 
shunt or compound machines, w^hen engines regulate 
poorly, or in machine shops and other places where 
trouble from grounds or short circuits on large motor 
units are frequent occurrencies, is shown in Figure 



J J J J i J J J 

n i\ TiTi'w n 




JLi jp i i f JLi 



11111 




Figure 79 

79. In many machine shops, for instance, the capac- 
ity of the motors connected is four or five times as 
great as that of the generators. The assumption is 
that only a small part of the motors will ever be op- 
erating at the same ime. When, however, the motor 
load exceeds the capacity of the generator, as it some- 
times does, the generator fuses blow and place the 
w^hole installation in idleness. This is also likely to 
occur in case of trouble on a single large motor, such 
as are used for metal saws, etc. For the above reasons 
it is preferable to divide the plant into sections, as 



Dynamo Operation — Direct Current 119 

shown. It will be noticed that any or all of the load 
may be thrown onto either set of machines by means 
of the throw over switches in the center row. Any 
desirable division of the load can thus be made. Office 
lights, for instance, can be separated from the large 
motors that are constantly disturbing the equilibrium 
of the lines. 

In transferring motors from one machine to the 
other it is necessary to allow time enough for the au- 
tomatic release to operate before the switch is closed 
on either set of bus bars, otherwise the motor is likely 
to be subject to a severe rush of current if its speed has 
fallen off much in the interval. If the motor is run- 
ning light and has great momentum, the switch can 
be thrown over quickly without much fear of dis- 
turbance. 

Shunt or compound dynamos if running singly, 
and if not supplying motors, may be shut down by 
simply shutting off the engine and letting them come 
to rest. If, however, there are motors connected to 
the dynamo, these must be disconnected before the 
voltage of the dynamo is allowed to go down. A mo- 
tor heavily loaded may stop entirely when the E.M.F. 
at its terminals drop off, say twenty-five per cent. It 
will then be without counter E.M.F. , and the arma- 
ture will form a dead ^^ short" which will blow fuses. 
The automatic release on the rheostat must not be re- 
lied upon in a case like this. 

If there are several dynamos operating in parallel 
and one is to be shut down, it must be disconnected 
from the switchboard while nearly at full pressure. 
The pressure may be reduced only sufficient to trans- 



120 



Operating and Testing 



fer the greater part of the load upon the machine 
which is to remain in service. If it is reduced more 
than this, the dynamo will be run as a motor by the 
other machine. 

COMPENSATORS 

Compensators, equalizers, or balancing coils are 
used in connection with high voltage generators to 
allow of the operation of lights or other devices at 
half the voltage of the dynamo. They also come in 




if^=F 



Figure 80 

convenient for the operation of variable speed motors 
since they make two voltages available. 

Figure 80 shows the connections of the system used 
by the Westinghouse Co. The armature of the dy- 
namo is connected so that it can produce both alter- 
nating and direct currents. The main current is di- 
rect and there is just A. C capacity enough provided 
to take care of the unbalanced portion of the load, 
which is usually estimated never to exceed 25 per cent 
of the capacity of the generators. 



Dynamo Operation — Direct Current 121 



All full voltage apparatus is connected to the + ^^^ 
— buses, and the half voltage equally distributed 
from the neutral and the two outside wires, so that 
the load will always be balanced as near as possible. 
The balancing coils B have the appearance of trans- 
formers, but carry no secondary winding. Their ob- 
ject is merely to provide a point at which only half of 
the voltage of the generator shall exist. Once properly 
connected they require no further attention except 




Figure 81 

to see that the load is not unbalanced beyond their ca- 
pacity. 

As more or less of the load may come on either 
side of the dynamo the compound winding is divided 
between both sides of the generator, which makes it 
necessary to run two equalizer wires, as shown. An 
ammeter for each dynamo lead should also be pro- 
vided. Volt meter and shunt field connections are 
not shown in this figure, as they are the same as with 
ordinary generators. 



122 



Operating and Testing 



The connections of a balancing set as arranged by 
the Y\"estern Electric Co. are shown in Figure 81. 
Here two differentially wound motors are connected 
to the same shaft, so that they must run at the same 
speed. So long as the same number of lights are burn- 
ing on both sides of the neutral wire the current 
through both motors is the same, and they perform no 
w^ork, but keep in motion. 



>^ 



n: 



^ 



o- 






'f^ 



^— , 



T 



^ 



-wmm 
+ 



t ..... 
~imm~ 



Figure 82 



The action of the set can best be comprehended from 
observation of the elementary diagram, Figure 82. 
With the load unbalanced as shown, current from the 
generator will pass through motor A and supply some 
of the excess load on the opposite side. As this cur- 
rent is in opposition to the shunt fields, it will weaken 
the motor fields and hence speed it up. This speeding 



Dynamo Operatmi — Direct Current 123 

up will also affect the other motor, the fields of which 
are not weakened, and hence cause it to act as a gen- 
erator, thus helping to supply some of the excess load. 
If the excess load appears upon the other side the 
conditions will be reversed. Either motor may act as 
a generator or motor, as conditions require. 

The field rheostat is used to equalize the voltage of 
the two machines and should be placed in the stronger 
field. Very often the coil on the starting box serves 
to unbalance the fields and must then be arranged on 
the opposite side from the field rheostat. 

In old installations the capacity of compensators is 
sometimes overtaxed by the addition of too many 
lights or motors. In such a case an artificial balancing 
load is often added, as shown at L. The lamps there 
shown may be connected to either side of the system, 
as the case may require. 

Storage batteries, as shown in Figure 128, can also 
be used for purposes of balancing as above. 



CHAPTER XI 

OPERATION OF ALTERNATORS 

The operation of a single phase alternator working 
alone is not much different from that of a direct cur- 
rent machine. Such machines may be compound 
wound, as illustrated in Figure 53, in which case that 
part of the current which circulates around the fields 
must be made to circulate always in the same direc- 
tion, as in direct current machines. This is accom- 
plished by means of the rectifier shown in Figure 53. 
Each of the sections of the rectifier are in connection 
with one of the collector rings and subject to c]ianges 
in the direction of current in the same way as the 
collector rings. The rectifier is mounted upon the 
same shaft as the armature and moves with it in such 
a manner that whenever the current in the armature 
falls to zero the change of brushes from one section 
to the other occurs. 

So long as the brushes are set in this position there 
is no sparking, but since there is considerable varia- 
tion in the inductance of an alternating circuit the 
current is not always at when it should be and, 
therefore, dt times there is very severe sparking. 
Compound wound alternators are, therefore, not much 
used at present. 

124 



Operation of Alternators 



125 



Some generators have two brushes in each lead of 
the rectifier. The trailing bnish is set permanently 
and the leading brushes alone are changed with 
changes in the inductance of the load. All alternators 




Figure S3 

are separately excited by means of a direct cutrent 
dynamo and the first step, therefore, is to bring this 
exciter in running order. This is done in the same 
manner as with shunt dynamos previously explained. 
Figure 83 shows two alternators connected to a 



126 Operating and Testing 

switchboard. The instruments are operated through 
suitable transformers, as is customary with high ten- 
sion installations. Both machines are excited by the 
same dynamo, but each, of course, has its o\^ti field 
rheostat, and there is a third rheostat for the exciter. 
The operation of alternators in parallel, though prac- 
tical, is somewhat difficult, and requires close atten- 
tion on the part of attendants; it is therefore often 
avoided, and the switchboard shown is divided so that 
each machine can take care of part of the load without 
being connected to the other. By means of the over- 
throw switches any or all of the lights or motors may 
be connected to either of the machines. Transfer 
from one machine to the other may be made at any 
time without shutting down motors, provided, of 
course, the machine will not be overloaded thereby. 
If a very large motor, however, happens to be heavily 
loaded, it is best to shut it down and start it again 
after transferring. 

In order to operate alternators in parallel, several 
precautions are necessary: 

They must all run very closely at the same speed 
and the fluctuations in speed must vary in about the 
same degree and occur at the same time. 

The E.M.F.S of the machines must be the same and 
they must be synchronized, i. e., they must pass 
through their respective maximum and minimum val- 
ues at the same time. In order to get a clearer under- 
standing of this refer to Figure 84. This figure shows 
two series of sine curves, which represent the currents 
of two machines. Both machines are working at the 
same E.M.F., but'the one represented by the lower part 



Operation of Alternators 127 

of the figure moves through eight cycles in the same 
length of time that the upper passes through seven. 
Beginning at the left the polarities of the dynamos are 
exactly opposite at the same time and there can, there- 
fore, be no cross currents between them. Gradually 
the lower machine gains on the other until at the cen- 
ter of the figure one is positive and the other nega- 
tive; at this point they are working in series instead 
of parallel, which is equivalent to a dead short cir- 
cuit, so that all of the current circulates between the 
two machines and none of it goes out to the line. Con- 

V\NW\N\j 

Figure 84 

tinning still farther at the right, they are again op- 
posed to each other and working in parallel. It v/ill 
be seen at once that two dynamos working in this 
manner cannot be coupled together without cau.^^ing 
serious damage to both of them. 

In order to attain smooth and economical operation 
it is necessary that both machines keep together in 
speed at all times. If they are nearly so a sliglit cur- 
rent from the leading machine passing into the lag- 
ging one will help operate it and thus speed it up to 
keep pace with the olher, but the less of such a cur- 
rent is necessarv the better it is. 



128 Operating and Testing 

If such dynamos are operated from a common shaft 
it will be well to leave the belt of one of tliem ?lack 
so that the other can easily force It into syaehronism. 
If they are operated by separate steam engines, the 
piston strokes of the engines should be synchronized. 
Eeferring to Figure 85, it can be seen that the engine 
receives nearly if not all of its power during the time 
that the crank pin is moving from 1 to 2 and from 3 to 
4. During the time it is moving from 2 to 3 and 4 to 1 
the steam is not only shut off, but some of it actually 
forms a cushion, which checks the motion. AVhile 
these differences in speed caused in this way are not 




Figure 85 

perceptible to the eye, they are sufficiently great to 
cause very damaging cross currents to circulate be- 
tween the dynamos. 

There are some specially designed machines that 
do not require such close synchronization. Such ma- 
chines are provided for operaiion in connection with 
gas engmes. These engines often miss fire and drop 
the whole load for an instant, and it is no unusual 
thing to see the ammeters of such machines swinging 
from zero to the maximum. 

In operating two alternators in parallel we begin 
by starting the first one, bringing it up to its proper 
voltage and speed and giving it about the load it 



Operation of Alternators 



129 



should ca»ry. The other machine is next started and 
if it has not been tried before the first step is to test 
it for polarity, i. e., to see that similar poles of both 
machines connect to the same bus bars. The simplest 
method of doing this is shown in Figure 86, but this 
method must not be used with high tension work. If 
the polarity of the second machine is right, the lamps 
shown at L will all be bright and dark at the same 
time. If the machines should accidentally be in phase 
with each other, the lamps would be dark continually, 



fi 



1] II di 



4 



CVj 



no m on 



Figure 86 

but as this will probably never occur they will alter- 
nate between light and dark with more or less rapid- 
ity. If the lamps do not go up and down together, 
two of the leading wires from one of the machines 
must be changed until the lamps are operating to- 
gether. Lamps used for this purpose must be capa- 
ble of standing double the pressure of the system since 
the only time at which they will be bright is when 
the dynamos are coupled in series and at double volt- 
age. 



130 



Operating and Testing 



■ The polarity of the machines being in order, the 
next step is to bring them in synchronism. There are 
different methods of doing this, illustrated further on. 
so we shall give here one of the simplest methods, but 
one that is suitable for low voltages only. In Figure 
87 one synchronizing lamp is provided for each dy- 




Figure 87 

namo, as shown. Suppose dynamo A to be running 
and that B is to be put in parallel with it. By closing 
the switches 1, 3 and 4, circuit is established through 
the two lamps and similar phase wires on the two ma- 
chines and the lamps are connected to two similar 
wires. If the voltage of the two wires is the same and 
the maxima occur at the same time the lamps will be 



Operation of Alternators 131 

dark and remain dark as long as the above condition 
prevails. But if one machine moves faster than the 
other, the same effect described before will be noticed 
on the lamps, viz : they will alternately light up and 
become dark. The nearer synchronism the two ma- 
chines are the longer will be the periods of light and 
darkness. The new machine must now be regulated so 
as to bring it nearly to the same speed as the other, 
and at about the middle of one of the dark periods 
when they are of several seconds duration the switch 
may be thrown in and the dynamos allowed to work 
together. 

It is not possible to divide the load between alterna- 
tors by simply raising the voltage of one machine, as 
is done with direct current machines. In order to 
increase the current in one of the machines, the engine 
driving it must be made to do more work by giving it 
more steam, and a governor by which this can be done 
must be provided. Giving an engine more steam will 
cause it to speed up a little and thus create a slight 
cross current, which will help drive the other. If a 
very great load is to be shifted from one dynamo to 
another, it is best to speed up the dynamo as above 
and also to increase its voltage a little, and to perform 
both operations by small steps, a little increase in 
power, then a little increase in pressure, a little more 
power and a little more pressure, etc. 

The currents circulating between two machines dif- 
fering only in voltage are wattless and do nothing but 
heat the wires. In order to get the best distribution 
of load an indicating watt meter should be placed in 
the circuit of each machine and the watts of both of 



132 Operating and Testing 

them kept in proportion to the capacity of the ma- 
chines. If such instruments are not at hand there must 
be an ammeter for each, and there should be a main 
line ammeter which measure the total current. If the 
sum of the machine currents is greater than the total 
line current, it is an indication of cross currents flow- 
ing between the machines. The dynamos must be sc 
adjusted that the sum of the dynamo currents becomes 
a minimum. When this is the case the cross currents 
are at their lowest value. 

The rheostats of the different machines should be 
worked in such a manner that the voltage of the line 
is not affected more than absolutely necessary while 
distributing the load. This is done by working the sev- 
ral rheostats a little at a time ; increasing one and de- 
creasing another, thus trying out how best the load 
can be distributed without changing the voltage of the 
system. If there is a power factor meter for each 
machine, they should be made to read alike and this 
will indicate that the machines, are working properly. 

Some of the larger systems using alternating cur- 
rents have two systems of bus bars that may be used 
in parallel or may be separated when occasion re- 
quires. "When such are to be connected in parallel 
there are two groups of generators to be synchronized 
instead of single machines. This is generally accom- 
plished by taking one or more generators out of service 
of the group which is running at the higher speed. 
This forces the total load on one engine less and thereby 
causes the whole group to run slower. When thus the 
two groups are in synchronism they may be coupled 
together. 



Operation of Alternators 133 

Rotary converters are operated in the same manner 
as alternators. They must be first brought up to speed 
by means of some outside source of power, usually an 
induction motor, or from the direct current side, and 
then synchronized. If there are several such convert- 
ers, the load must be divided between them by 
strengthening the field of the one that is to take more 
current. 

By proper manipulation of the excitation the power 
factor of a given load can also be materially affected 
and occasional attempts to improve it will do no harm. 

The power factor of a line indicates the ratio of the 
true power transmitted to the apparent powder. To 
find the real power being delivered by an alternating 
current system, we must multiply the product of the 
volts and amperes by the power factor. The power 
factor of a system supplying incandescent lights only 
is ordinarily about .95 while wdth induction motors it 
is often as low as .70, especially if the motors are not 
used at proper load. Whenever the power factor is 
low, the system is operating at poor efficiency. 

Long distance transmission lines are frequently de- 
signed for very great losses at full load. In such a 
case the voltage will be too low for satisfactory opera- 
tion when the full load is being used and if, to over- 
come this, the pressure of the dynamo is raised it will 
be too high on circuits that are not heavily loaded. 
In order to obtain satisfactory operation under such 
circumstances some means must be provided whereby 
the pressure on different branch circuits can be reg- 
ulated without changing the voltage of the dynamo. 

The Stillwell regulator is the best known of these. 



134 



Operating and Testing 



and is typical of all the others. Each regulator must 
be provided with two windings and is really a trans- 
former, the primary circuit of which is connected 
across the mains and the secondary in series with the 
main current. In Figure 88 S is a double throw 
switch, by means of which the primary coils Y can be 
connected so as to raise or lower the voltage of the line. 
By means of the handle C as much of the secondary 
winding can be inserted into the main circuit as may 
be found necessary, and this may assist or oppose the 
main line voltage. The inductance L is provided to 




Figure 88 

prevent serious short circuiting of any of the secondary 
coils while the contacts of C are moved from one seg- 
ment to another. It will be seen that C is split and 
tiiat therefore during the time that it bridges two seg- 
ments the currents induced in the coil between them 
must pass through L. 



SYNCHRONIZERS 



To connect a direct current generator in parallel 
with a generator already running the voltage of the 



Operation of Alternators 135 

generator to be connected must be adjusted to corre- 
spond with the' voltage of the generator which is run 
ning, or with the bus bars to which the generator is 
connected. When their voltages are alike the generator 
circuit may be closed. 

AVhen alternating current generators are connected 
in parallel, the geneartor to be" connected must not 
only correspond in voltage, but it must also be in ^^syn- 
chronism" with the other generators feeding into the 
bus bars. Two alternating currents are in synchro- 
nism when their phases coincide, or when all changes 
in their E.M.F. 's exactly correspond. Both must reach 
a positive maximum value at exactly the same time. If 
two generators were connected together when their 
E.M.F. 's were 180° out of phase, or when the E.M.F. 
of one machine was at a positive and the other at a 
negative maximum for instance, a direct short circuit 
would occur. The conditions would then be very simi- 
lar to those existing where a direct current generator 
with its polarity reversed was thrown in parallel with 
another machine. The positive of one machine would 
then be connected directly to the negative of the re- 
maining machine and a severe short circuit would re- 
sult. 

Where the currents of two alternators are only 
slightly out of phase, the incoming machine will be 
brought into step with those already running, but a 
considerable strain will be imposed on all the machines 
and considerable current will flow between them. In 
order to ascertain when two alternators are in synchro- 
nism, synchronizers are used. The simplest form of 
synchronizer consists of two incandescent lamps con- 



136 



Operating and Testing 



nected in series between the machines as shown by 
broken lines in Figure 89. 

If the brushes bearing on the same collector rings 
are to be connected together, or to the same bus bar, it 
is evident that when the two machines are in phase, or 
synchronism, the two brushes will at any moment be at 
the same potential and of the same polarity. The 
E.M.F.'s of the two generators being directly opposed 
the lamps connected between them will not burn. This 



m,r ^ 


i, 


^ 




1 








\ 


o (S 








A/^ 






1 1 


^ 


\ 


r-i 


I 1 


D"! 








g 


r S 


f 







1 I 










LjB HJLJ 




f 


r 




f 


^ 








c 


tt 


3 


1 


m 


t 








. 


KgJ 


r 



Figure 89 

is called s\TLchronizing '^dark," due to the fact that 
the lamps remain dark Avhen the generators are in step. 
Suppose the currents in the two generators were 180^ 
out of phase. AVhen one of the collecting rings of ma- 
chine L is positive, the corresponding ring of machine 
M is negative and the two machines are then generat- 
ing in series. The two lamps will, therefore, bum at 
full candle power, the combined E.M.F.'s of the two 
generators being now impressed on the lamps. Two 
lamps of the same voltage as the generators or one 



Operation of Alternators 137 

lamp of a voltage suitable for the combined voltage of 
the two generators may be used. 

If the two generators continued to run under the 
same conditions as those just described, and did not 
change in speed, the two lamps would continue to 
burn at full candle power ; but if one of the machines 
runs at a slightly slower speed, the positive maximum 
values of the E.M.F. of this machine would occur 
just a little later than that of the other, fmally falling 
back to a point where the two generators come again 
in synchronism, at which point the lamps would be 
dark. As long as the generators are varying in speed, 
the lamps will alternately light up and go out, this 
change occurring more rapidly as the difference in 
their speed increases and gradually dying out as they 
approach uniformity. As they approach synchron- 
ism the intervals between the time of light and dark 
will grow longer and when a point is reached where 
the lamps stay dark for a considerable time, the main 
switch may be thrown in and the machines run to- 
gether. 

In synchronizing alternators, it is safer to close the 
main switches just before the point of synchronism is 
reached than after, as some little time is required to 
throw in the main switches. 

In order that the lamps may be used w^ith either 
machine and w^ithout leaving them continually in con- 
nection with either of the machines they may be ar- 
ranged as shown in the center of the figure. The over- 
throw switch must be thrown towards the incoming 
machine. 

The use of synchronizing lamps, as shown in Figure 



138 



Operating and Testing 



89, is limited to low voltage^. Transformers may be 
connected in the generator circuit, as shown in Fig- 
ure 90. This arrangement allows the use of ordinary 
voltage lamps, irrespective of the voltage of the gen- 
erators. If the transformers are so connected that 
their secondaries oppose each other when the genera- 
tors are in step the darkness of the lamp will indicate 
the point of synchronism. If either one of the prima- 
ries or secondaries of the transformers are reversed 
the transformer secondaries will be in series and assist 
each other and the point of synchronism will be indi- 






Fignre 90 

cated by the lamp burning at full brightness. This is 
known as synchronizinz ''bright." Either method 
may be used and both have their advantages and disad- 
vantages. 

If both of the plugs used make the same connection 
as indicated at 1 and 2, the lamps will be dark at 
synchronism ; if one of the plugs reverses connections, 
as at 3, the lamps will be bright at synchronism. "When 
the machines are running together the synchronizing 
bus is entirely disconnected. When synchronizing 
bright, the eye becomes more or less fatigued by con- 
stantly watching the lamp and the point of full bright- 



Operation of Alternators 



139 



ness may be misjudged. On the other hand an incan- 
descent lamp requires considerable voltage before the 
filament becomes visible and darkness does not neces- 
sarily denote that no current is flowing, or the fila- 
ment may be broken during the time of synchroniz- 
ing. To overcome these objections mechanical syn- 

. [I 



m 



G 



s: 



H 



M 



tk 



F 




©2 

Figure 91 

chronizers have been devised and are now generally 
used, which will not only accurately indicate the ex- 
act point of synchrony but will also show which ma- 
chine is running too fast or too slow. 

The Lincoln synchroscope is a device designed for 
this purpose. The principle of its operation may be 



140 Operating and Testing 

nnderstood by reference to Fignre 91, where F rep- 
resents a stationary field supplied with current 
through the two lower binding posts on the instrument 
to one of the generators. The two coils G and H at 
right angles to each other, are mounted on a shaft and 
are free to revolve about their common axis. The 
windings of the movable coils are brought to a com- 
mon junction and carried to a slip ring mounted on 
the shaft, connection being made from this point to a 
binding post at the top of the instrument. The re- 
maining ends of the coils are carried to two other slip 
rings. Connected in series with one of the coils is a 
non-inductive resistance (incandescent lamp) and in 
series with the other coil an inductive resistance or 
choke coil. From these resistances the connections are 
brought to a common point and carried to the remain- 
ing binding post. 

Connection is made from the binding posts 1 and 2 
to one of the machines to be synchronized and from 
the other binding posts to the remaining machine. 
When an alternating current is passed through the 
movable coils, there will be a phase difference of 90° 
between the current in coil G and that in coil H, and 
a rotating magnetic field will result. This rotating 
field acting in conjunction with the rapidly reversing 
field of coil F will cause the movable coil to revolve. 
A pointer attached to the shaft of this coil indicates 
the direction and extent of the movement. 

As long as the two generators vary in speed the 
pointer will continue to revolve, turning at a greater 
rate with a greater difference in speed and slower as 
the generators approach synchronism. Should the 



Operation of Alternators 



141 



machine which was running faster, decrease in speed 
and run slower than the other machine, the pointer 
would revolve at a slower rate and finally run in the 
reverse direction. When the machines are running at 
exactly the same speed, the pointer will come to rest. 
If the machines are in phase the pointer will come to 
rest in an upright position ; if out of pha^e, the posi- 
tion of the pointer will indicate the difference in phase 
between the currents in the two machines. 




Figure 92 



Synchronizing lamps are often used in connection 
with synchronizers. If the difference in speed be- 
tween two generators is great, the instruments do not 
always indicate right, and for this reason the synchro- 
nization is started with the lamps and finished off with 
the instrument. In connecting up a synchroscope it 
should always be checked with lamps to see that it 
indicates right. If it does not, some of the wires must 
be changed until it does. 



142 



Operating and Testing 



Figure 92 shows the switchboard connections of the 
Westinghouse synchroscope arranged for high poten- 
tial. V T are the voltage transformers, one for each 
machine, P the plug receptacles and L the synchroniz- 
ing lamps. 

The power factor meter is similar in principle to the 
synchroscope and the switchboard connections for two 
phase are shown in Figure 93, and for three phase in 
Figure 94. If necessary a voltage transformer is cut 
into the circuit, as indicated by dotted lines. Three 





Figure 93 



Figure 94 



lamps cross connected between the three phases as 
shown in Figure 95 can also be used for synchronizing 
in connection with three phase circuits. 

Let the two halves of the figure at the right and 
left each represent a dynamo, both of which are to be 
operated together. If both are running at the same 
speed they will be in synchronism and whatever rela- 
tion as to brilliancy between the different lamps may 
exist at any moment will exist at all times, i. e., the 
lights will work in unison either up or down. If, 
however, one of the machines is moving faster there 



Operation of Alternators 



143 



will be a steady change in all of the lights. To get a 
clearer view of this let the machine at the right be 
moving twice as fast as the one at the left. The 
E.M.F.s of the two machines will then at any time be 
represented by the length of the line measured from 
A, B, C, either up or down until it intersects the sine 
curves. 

To find the brilliancy of any of the lamps A B C we 
must note the difference of potential between the 



5 6 7 8 




Figure 95 

phases to which it is connected. If both E.M.F.s are 
above the horizontal line they must be subtracted, the 
lesser from the greater, if one is above and the other 
below the values must be added, since they represent 
opposite polarities. Following this out we obtain the 
table below in which the numbers stand for relative 
brilliancy, representing darkness and 14 the highest 
obtainable voltage which is double that of one dynamo. 



144 



Operating mid Testing 



The numbers 1, 1, 2, 2, etc., indicate the advance in 
speed of one machine over the other, that at the right 
moving twice as fast as the other. 



TABLE A 





1-1 


2-2 


3-3 


4-4 


5-5 


6-6 


1 7-7 1 


8-8 


A 


6 


11 


2 





5 


4 


2 


13 


B 


6 


14 


9 


6 


11 


3 





3 


C 





6 


4 


5 


13 


1 11 


1 3 


11 



AVith conditions as above the lamps will light up in 
the order A, B, C. If the machine at the left moves 
faster than the other the lamps will light up in the 
order C, B, A and thus give an indication as to whether 
the incoming machine is running too fast or too slow. 



CHAPTER XII 



MOTOR OPERATION 



We have already seen that the ordinary direct cur- 
rent motor requires some resistance in the circuit at 
starting to prevent an excessive r^osh of current during 
the time the armature is developing the necessary 
counter E.M.F. 




Figure 96 

One of the best rheostats for this purpose used in 
connection with shunt or compound motors is illus- 
trated in Figure 96. This rheostat is equipped with 
' ' overload ' ' and ' ' no voltage ' ' releases. Both of these 
are necessary to protect the motor properly but it is 
possible to operate motors without them as the ordi- 
nary fuse, if of proper size, will take care of the 
motor. An overload will cause excessive current to 
pass through the armature and a drop in voltage will 
do the same thing especially if it is sufficient to cause 

145 



146 Operating and Testing 

the motor to come to rest, in which case the armature 
becomes a short circuit and will rapidly burn out. 

Referring to the diagram, current enters at 1 and 
passes through magnet 2 and the arm A of the rheo- 
stat. Here the circuit is open until the arm is moved 
to the right ; when the arm touches the first point of 
R current begins to flow through all of the resistance 
and the armature and at the same time through the 
fields. It is important that the conections be so made 
that the field is fully excited before the armature re- 
ceives much current as the current will flow through 
the armature much more rapidly than through the 
fields. It will be seen that the field current passes 
through magnet 3 and when the arm is finally brought 
to the last point this magnet engages an iron armature 
on the arm A and thus holds it at that point as long 
as current flows through the magnet. Should the volt- 
age of the circuit drop off considerably the magnet 
will be unable to hold the arm and a strong spring 
attached to it will force it back to the off position. 
Should the motor be overloaded the armature of mag- 
net 2 will be drawn up and close the circuit at 4; 
this will shunt the current around magnet 3 and cause 
it to release the arm which will then fly back. If 
desired, push buttons or switches can be attached to 
this shunt circuit in the same manner at different 
places, so that the motor can be stopped from any of 
these points. 

Attention is called to the manner of connecting up 
this rheostat ; it will be noticed that the field circuit 
is never entirely opened. This is an important feat- 
ure as it prevents much of the destructive sparking 



Motor Operation 147 

which always occurs when a circuit containing electro- 
magnets is opened. It also saves the insulation of the 
motor from many very severe strains as a very high 
E.M.F. is developed for an instant when the field cir- 
cuit is broken. AYith this connection this is avoided 
and the field discharge passes through the armature 
which acts as generator through this circuit until it 
comes to rest. If the switch on a motor provided with 
a rheostat as shown is suddenly opened the arm of 
the rheostat will not fly back at once but will be held 
in place by the current generated by the armature for 
a few moments until it comes nearly to rest. 

The rheostat should always be located so that the 
action of the motor can be observed from this place ; 
if belting, etc., connected to the motor can be seen 
from the rheostat it will answer the purpose. 

The first step in starting a motor is to close the 
main switch; next move the arm of the starting box 
slowly and note whether the armature begins to move. 
If it does not do so it is not safe to continue movement 
of the arm, but instead it should be returned and the 
cause of the trouble located. (See Motor Troubles.) 

Ordinarily not more than 30 seconds should be con- 
sumed in moving the arm from starting position to 
position of rest. If more time is taken the rheostat 
coils are likely to burn out. This of course depends 
very much upon the load the motor may be carrying 
when starting. If the arm is moved over too fast the 
armature is likely to burn out. This also depends 
greatly upon the load it may be carrying at the time. 
Durinor the time of starting and immdeiately after- 
ward the condition of the brushes should be noted and 



148 Operating and Testing 

they should be adjusted to point of least sparking. 
Good modern motors should not spark at all. Motors 
equipped with starting boxes like the above will gen- 
erally take care of themselves if for any reason the 
current should fail. If the starting box is not auto- 
matic the switch of the motor should be opened at 
once in case the current fails ; a sudden coming on of 
the current would either blow fuses or burn out the 
armature. Motors with such starters should also be 
disconnected from the service before the generators 
are shut down at noon or evening. This may be done 
either by the attendant at the motor or by the man in 
charge of the switchboard. In all larger, well man- 
aged installations it is customary to have certain men 
detailed to stop and start all motors at the proper 
time. 

Series motors, such as are used on street railways, 
cranes, etc., unless specially wound or used in connec- 
tion with a very steady load require constant attention 
and cannot be operated unless an attendant is always 
at hand. 

ALTERNATING CURRENT MOTORS 

Alternating current motors fall into three general 
classes: Single phase induction motors; polyphase in- 
duction motors; synchronous motors. The single 
phase induction motor requires some artificial means 
of starting, as illustrated in Figure 63. The direction 
of rotation can be varied by reversing the connections 
of either one of the two windings. 

The smaller of these motors require no starting 
boxes. At starting they draw a very heavy current, 



Motor Operation 149 

usually from 5 to 6 times the running current, but 
this soon ceases. 

"With the larger motors up to 5 H.P. the switching 
arrangement shown in Figure 65 may be used. This 
switch is shown three phase but may be used equally 
well with single phase. The switch is thrown to the 
up position and held there until the motor has gained 
considerable speed and the heaviest rush of current is 
over ; it is then thrown downward and the motor con- 
tinues to run but now under protection of the fuses. 
This throwing over of the switch must be quickly 
done so that the motor will not lose much speed 
in the interval during which it is without current. 

If an induction motor is overloaded it will often 
come completely to rest and burn out. 

The motor most commonly used for power purposes 
is the 3 phase motor. Two phase systems are not 
much used. This motor is self starting and requires 
no help in this respect. But like the single phase 
motor the currents required at starting are very much 
greater than the running current. It is therefore 
customary to use the same starting devices as with sin- 
gle phase motors, but as this type of motor is used 
in much larger units than the single phase better 
\ starting devices are furnished. 

Figure 69 shows a diagram of an auto starter used 
with 3 phase motor. So long as the switch is in the 
position sho^^^l the current must pass through the re- 
actances 1, 2, 3, and these prevent the heavy rush 
of current which would take place otherwise. After 
the motor has attained nearly its running speed the 



150 Operating and Testing 

switch is throAMi up and the motor receives the full 
line pressure. 

It is always best to arrange such motors so they can 
be started without load. 

With larger sizes of induction motors the rotor is 
often w^ound. In such cases a resistance may be 
placed in the motor circuit and operated as with direct 
current motors. The resistance may be fully cut out 
when the motor attains full speed (See Figure 68.) 

Three phase motors may be reversed in direction by 
changing the relative position of any two wires leading 
into the motor. 

With all induction motors the efficiency is quite low 
unless the rotor is made with a very small air gap be- 
tween it and the stator. A very small amount of 
wear wdll therefore be likely to bring both in touch 
and ruin the motor. For this reason great care in the 
application of belts must be used ; too tight a belt will 
soon wear the journals and allow the rotor to come in 
contact with the stator. 

A three phase motor will not start unless all of the 
wires are delivering current, but it will continue to 
run if one or two of the phases are out of circuit. 
Under these conditions, however, it will draw very 
heavy currents and very likely burn out. 

Polyphase synchronous motors, if there is no other 
way, may be started by allowing current to flow in the 
armature w^hile the field circuit is open. This method 
gives rise to much trouble and is not to be recom- 
mended. Such motors should be brought up to speed 
and started like alternators running in parallel. (See 
Sjaichronizers and Operation of Alternators.) 



CHAPTER XIII 

TRANSFORMERS 

The losses of energy in an electric circuit are pro- 
portional to the current flowing. The power trans- 
mitted is proportional to the product of the current 
and pressure-amperes and volts. Bearing these two 
facts in mind, we can easily see that to reduce losses to 
a minimum we should work with a minimum current, 
but as we decrease the current we must increase the 
voltage in the same ratio. To transmit a given amount 
of power, if we divide the current by 2, we must multi- 
ply the volts by 2. 

High electrical pressure, it is well known, is quite 
dangerous, not only to human life, but there is also 
considerable fire hazard with it and it is furthermore 
impracticable to use it in many places where, for in- 
stance, insulation is difficult. This fact again makes 
it desirable to avoid the use of high pressures where it 
is likely that inexperienced humanity may come in 
contact with it. 

In the electric transformer we have the means of 
using electrical pressure at a low potential, if neces- 
sary, inside of buildings, increasing that pressure to 
a great extent out of doors and reducing it again to a 
safe potential when w^e enter the premises w^here power 
is to be used. 

151 



152 



Operating and Testing 



Since we can raise the pressure to a great extent on 
that part of the line which is pretty well out of reach 
of most people, we need but a correspondingly small 
current and can, therefore,^ get along with correspond- 
ingly small wires. 




Figure 97 



An illustration of such an installation is diagram- 
matically shown in Figure 97. The transformer T 
nearest the dynamo is known as a ''step up" and the 
other as a ^'step down" transformer. A step up 



wvwW 




mmm 

mmmm 




Figure 98 

transformer is not always used, very often the full 
line potential, is generate direct by the dynamo. On 
the other hand, in many cases a double transformation 
is required as illustrated in Figure 98. This only as 



Tmnsformers 153 

a safeguard, however, as it has no operating advan- 
tages ; it merely reduces the liability of breakdown iu 
the insulation. 

A complete comprehension of the transformer re- 
quires a knowledge of the phenomena of electrical in- 
duction and inductance and without this knowledge 
one cannot intelligently operate or test transformers. 
The term ^^ electrical induction" describes the induc- 
ing of one current by another. "We are already some- 
what familiar with the phenomenon of lines of force 
cutting wires, but it will do no harm to touch upon 
this subject again. 




Figure 99 

Referring to Figure 99, if a current is started in 
one of the closed circuits. A, for instance, it will set 
up lines of force encircling the wire as indicated 
by the arrow, B. These lines of force we know re- 
quire power to create and oppose the current which is 
creating them. So long, however, as their only chance 
of action is on the same conductor in which the cur- 
Tent which gives rise to them flows, their only effect 
is to retard or check the current flow as long as they 
are increasing in number. After they have attained 
a steady value, they no longer retard the current, in 
fact have no further effect on it until they begin to 
decrease in number again. If, however, these lines of 



154 Operating^ and Testing 

force are in position to ^^cut," i. e., to encircle another 
closed conductor, they at once give rise to currents in 
it and these currents since they are created by a force 
\vhich opposed the original current or force must, of 
course, be in opposition to it. Thus it is that when- 
ever two closed conductors are laid side by side and a 
current is set up in either of them, another current 
opposing the first will be set up in the other circuit. 
Thus the first current is said to induce the other and 
is spoken of as an inducting or primary current, while 
the other is known as the induced, or secondary cur- 
rent. The phenomenon above referred to is that of 
electrical induction and every change in current 
strength and direction in one such conductor will be 
followed by a corresponding change in tJtie other. 

We have seen how an electric current induces an- 
other current in a neighboring conductor if that con- 
ductor is part of a separate coil. Similar induction 
also takes place in wires belonging to the same coil, 
as these are also cut by the same lines of force and as 
this opposes the original current, it gives rise to what 
is known as the counter E.M.F. of self-induction, or 
self induction, or inductance. 

We have now a clear view of these two phenomena ; 
that the primary coil tends to induce currents in the 
secondary coil and also opposes itself. We have also 
seen in previous chapters that both of these effects are 
largely increased if the wires are wound upon an iron 
core having high magnetic conductivity. AVith every 
good transformer there is a magnetic circuit of very 
high conductivity, so that the self induction of the 
primary circuit is very great. In fact, it is the aim 



Transformers 155 

of all builders to make it so great that very little 
current will flow while only the primary coil is con- 
nected. 

Now let ns examine the effect of the secondary coil. 
"We know that the primary coil induces currents in it 
which flow in opposition to those in the primary. Fur- 
thermore, it is evident these currents must react upon 
the primar}^ in just the reverse direction that the pri- 
mary currents react upon themselves, in other words, 
they tend to lessen the self induction of the primary 
coil and bring about a greater current flow in it. The 
secondary coil also, of course, reacts upon itself, but 
this reaction is again balanced by the greater action 
of the primary. Thus the whole current flow in a 
well designed transformer is governed by the second- 
ary coil. If it is an open circuit, no current flow^s ; if 
one light is turned on, there is some flow ; if more are 
turned on, the current is in proportion, all of course 
within the range of the carrying capacity of the wires. 
This interaction of the two currents is called ^^ mutual 
induction" and it is this interaction which makes the 
transformer so useful and efficient. 

In practice the electric transformer consists of an 
iron core upon which two separate coils of mre are 
wound. 

These t«wo coils must be insulated from each other, 
but should otherwise be as close together as proper re- 
gard for safety w^ill permit. One of the coils of wire 
is usually subject to much higher pressure than the 
other and there is always danger of the insulation be- 
tween them breaking down. Many fires and some 
loss of life have been caused by this. 



156 Operating and Testing 

In Figure 100 there is shown a diagrammatic illus- 
tration of a transformer having a ratio of 10 to 2 ; by 
this is meant that the number of turns of wire in one 
coil is 5 times as great as in the other ; wath this ratio 
the voltage in the coil having the most turns will be 
5 times as great as in the other, while in the other the 
current will be 5 times as great as in the first. In 
both coils the power will be the same, if they are 
properly designed; if we neglect the losses due to 
heating hysteresis, etc., which, however, in large well- 
designed transformers, should not be over two or 





Figure 100 



three per cent and if they are operated on full load 
even less. 

In order to see more clearly that the power in both 
coils is the same, w^e must bear in mind that the sec- 
ondary coil can deliver no more power than it re- 
ceives from the primary and (supposing a transformer 
of 100 per cent efficiency) the primary coil must be 
of such self induction that no current whatever will 
flow as long as the secondary coil is on open circuit- 
Hence the primary can deliver only enough power to 
provide what the secondary is taking and the power 
in the coils must be always the same. 



Transformers 



157 



The losses in the transformer are due : First, to the 
ohmic resistance of the coils ; second, to inefficiency of 
the magnetic circuit provided by the iron core ; third, 
to eddy or foucault currents generated in the iron 
core and also in the copper wires themselves (this is 
very small), and fourth, to hysteresis. 

As transformers grow old, they are very apt to 
lose in efficiency, although some makers have recently 
produced iron which it is claimed does not deteriorate 
with age. 




Figure 101 

The losses due to ohmic resistance can be reduced by 
using larger wire of higher conductivity. The losses 
due to foucault currents are kept at a minimum by 
''laminating" the iron core of the transformer. Since 
foucault currents are induced by lines of force which 
act at right angles to the inducing current, they must 
flow in the same general directions as the currents 
which produce them, hence, to introduce as much re- 
sistance as possible into their circuit (which is the 
iron core) it is built up of thin washers insulated from 
each other, sometimes by thin paper, often by merely 



158 



Operating and Testing 



the oxidization on the sides of the plates. The rela- 
tive position of wire and plates is shown in Fi^re 
101 ; arrow 1 shows direction of inducing current, 
arrow 2, direction of lines of force and arrow 3, dire^'-- 
tion foucault currents would take if the insulation 
between the laminations did not prevent them. 



VWA/ 





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-mmm-^ 



Figure 102 



Transformers are connected- in series sometimes, as 
sho\\TL in Figure 102. As a rule transformers con- 
nected this way are small, each supplying only a few 
lights. 



WWW 

mmm 




Figure 103 

The majority of transformers are connected in par- 
allel, as illustrated in Figures 103, 104 and 105. 

Figure 103 is the simplest and requires no other 
testing than to determine which is the primary wire. 
This is usually easily determined by simply noting the 
size of the two pairs of wires which project from the 
transformer, the smaller being the primary. Should 



Transformers 



15S 



these wires be identical in size, the resistances of the 
two coils should be measured. Tliis can be done with 
a wheatstone brido^e or with a voltmeter, the volt- 



■o 
o 
-O- 



-o 



o 



WWVvM/WVW 

Hmmm m^ 



wwvwvw 





Figure 104 



Figure 105 



meter test being made as shown in diagram, Fig- 
ure 106. Use a low potential circuit and direct cur- 



1 



u 




wwv\ 



Figure 106 

rent if possible and allow no one to come in contact 
with the ends of the coils as a very high potential may 
be generated in one of them. 



160 



Operating and Testing 



The coil having the higher resistance will show the 
lowest reading on voltmeter and may be set down as 
the primary in case of a step down transformer and 
secondary in case of a step up transformer. 



O 



o 



o 
o 
■o 



» > :^ ► 

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wwwwwv\ 




Figure 107 



Wm/ www 




Figure 108 

Transformers are often connected so that their sec- 
ondaries may operate on the 3-wire system. Figures 
107 and 108 show the right and wTong connections. 
Both methods will operate the lights, but with the 
wrong method the neutral or middle wire will be called 



Transformers 



161 



upon to carry double current and the loss in the wires 
will probably be excessive. AYith the right method, 
both transformers will use only as much current as one 
would use, but they will have double voltage, 2 lights 
being in series. This method makes possible a great 
saving in wire. One can easily determine whether 
such a bank of transformers is connected right or 
wrong by connecting two lamps across the two outside 
wires without connecting to the neutral. If the lamps 



mmN 

MAW\ 



.n 



Figure 109 

burn properly the transformers are K. ; if they are 
connected wrong the lights will not burn at all. 

When transformers are banked either in parallel 
or in series it is necessary that their polarity be known. 
"With transformers of the same make, it is safe enough 
to assume that all are of the same polarity and to con- 
nect them accordingly. If, however, transformers of 
different make are to be run together, they should be 
tested and marked beforehand. To do this make con- 



162 



Operating and 'Testing 



nections to some direct current as shown in Figure 
109. A direct current applied to a transformer will 
cause one impulse to be given to the voltmeter or gal- 
vanometer shown in the secondary. On each trans- 
former mark that wire of the primary which gives a 
certain deflection on the voltmeter and in banking 
these transformers, see that these marked wires all 
connect to the same primary wire for parallel working. 
For this test a voltmeter whose deflections depend 
upon the direction of current must be chosen. 




NW\N\ /WVW\ /WVW\ 



Figure 110 

In Figure 110 another system of banking transform- 
ers is shown that often leads to trouble. If the prir 
mary fuse in one transformer ^^ blows," it is evident 
that current from the other transformers will circu- 
late in the secondary and thus add the transformer 
to the load in lights they have to carry, thus shortly 
causing other fuses to blow. Small transformers are 
far less efficient than large ones and this connection 
should not be used when it can be avoided. 

Transformers to operate with a given voltage and 
frequency must be designed for this. If a higher 



Transformers 



163 



frequency is employed than the transformer is de- 
signed for, its self-induction will be too great to per- 
mit current flow. If the frequency is less than called 
for by the transformer, it will generate excessive volt- 





www www 




Figure 111 



Fio^ure 112 



age and overheat the transformer unless fuses are 
blown. 

Two transformers of the proper frequency, but only 
one-half the voltage of the circuit may be operated 
in series in either of the ways shown in Figures 111 
and 112. 



pLpLp 




_AAAA . AAAA 



Figure 113 Figure 114 

Figures 113 and 114 shows methods of connecting 
three-phase transformers. Figure 113 shows what is 
termed the delta connection and Figure 114 the Y or 
star connection. The delta connection has the ad- 
vantage that the burning out of one transformer does 



164 



Operating and Testing 



not seriously affect the operation of the other two, and 
even when two transformers fail the third will still 
operate on one phase. This is not the case with the 
star connection, one transformer failing seriously 
hampers the whole group. 

Figure 115 is drawn to illustrate the voltage or cur- 
rent relations existing between star and delta con- 
nected transformers. S represents the star, and D the 



12 3 4 5 6 7 8 



i 




i 



i 



^ 



z 



il 






r^DO^' 



? 



I 



i 






Figure 115 

delta connection. Suppose the current be as shown 
by the curves under 1 at the left. At this instant 
phase A is at zero, and B is negative and equal to C 
positive. This leaves SI without current for an in- 
stant and S2 and 3 in series taking the voltage of two 
phases. Between 3 and 4 A has risen to its maximum 
positive and B and C are negative and equal. The 
total current now passes through SI and divides 
equally on the return through S2 and 3. At 5 A and 



Transformers 165 

B are both positive and C is at a maximum negative, 
thus taking all of the current coming through SI and 
2 through S3. The above relation of the current in 
the different phases will hold for all intermediate po- 
sitions and it can be seen that at no time is any one 
transformer coil subject to more than the current of 
one phase. 

If we take up the delta connection in the same way 
we shall notice that at 1 coil D3 is subject singly to 
the pressure of two phases. There being no pressure 
at A, at this point current is also passing through Dl 
and 2 in series. 




Figure 116 

A complete investigation of this shows that with a 
given circuit for star connection the individual trans- 
formers are subject to only .58 of the voltage between 
the phases necessary, or for transformers to be used 
with the delta connection. If the same transformers 
used for star are connected delta, the current required 
for the delivery of a certain amount of power will be 
1.73 times as great for the delta connection as for the 
star. While many transformers are so built as to be 
serviceable on either connection, it will not be safe to 
assume that all of them are and the operator should 
first inform himself on this point. 

Figure 116 shows the methods of connecting up 
distributed transformers on three-phase circuits. The 



166 



Operating and Testing 



three heavy lines denote the three-phase wires which 
carry the main current and the light line denotes a 
fourth wire used for balancing. This wire may be 
run all the way from the generators or may run only 
between the different transformers This wire is nec- 
essary when a number of transformers located some 
distance apart are to be connected star, but is not 
needed for delta connection. It is also not generally 
used where a bank of transformers are feeding a lot 
of motors or a big installation of lights. Whether the 
transformers are connected star or delta, or whether 
they are located close together or long distance 



rwwwn 



Figure 117 



Figure 118 



apart, it is always important to arrange so that the 
load may be as evenly as possible divided between the 
different phases. 

In some instances, to save the cost of one transformer, 
three-phase transformers are connected as shown in 
Figure 117. Many transformers are wound so they 
can be used with different voltages and current. The 
manner in which this is effected is illustrated in Fig- 
ure 118. If the ends A B and C D are joined the 
transformer-windings are fitted for but half the volt- 
age but double the current as could be used if C were 
joined to B. This latter connection places windings 



Transformers 167 

in series, while the former places them in parallel. In 
connecting two such coils in series care must be taken 
that current passes through both in the proper direc- 
tion, if the connection should be made A C D B one- 
half of the transformer would oppose the other. 

As it often happens that the insulation between the 
primary and secondary wires gives w^ay and thus great 
danger to life and property results, it is advisable to 
ground transformers, as illustrated in Figure 105, the 
ground wire C being connected to some neutral point 
on transformer. The shells of all transformers should 
be grounded. 

The principal losses in a transformer are the core 
losses, due to inefficiency of magnetic circuit, and the 
copper losses due to the ohmic resistance of the cop- 
per. 

The eflEiciency of a transformer can be determined 
by measuring the power supplied to the primary by a 
watt-meter and dividing the power obtained from the 
secondary by it. 

The core losses can be determined by measuring the 
current flowing in the primary while the secondary is 
open and noting the percentage of this current to the 
maximum current. 

The copper losses are found by short circuiting the 
secondary w^inding and applying voltage enough to 
the primary to cause the full load current in the sec- 
ondary. The greater the copper resistance, the more 
power must be supplied to the primaries. This power 
must also be measured with a wattmeter. Volt and 
ammeter measurements cannot be used with altemat- 



168 



Operating and Testing 



ing currents. This method is due to Dr. Sumpner, and 
connections are shown in Figure 119. 

Every transformer before being connected should 
be tested for insulation between the two coUs and each 
coil for insulation from the shell, as well as for conti- 
nuity. These tests can all be made with a wheatstone 
bridge. 

As high potential is nearly always used in connec- 
tion with transformers, great care is necessary in 



O 



3 



4=-^ 



o 



wwwwvw 

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Q 



Figure 119 

handling them. The following rules should be care- 
fully observed: 

Do not handle more than one wire at a time, and 
touch it only with one hand at a time. 

Wear rubber gloves and do not let them be moist. 

Keep yourself insulated from the ground and from 
all other wires. 

Do not place fuses in circuit until all connections 
have been made. 



Transformers 169 

Use enclosed fuses; a small rubber tube over the 
fuse wires is better than nothing. 

If working on a line that is ^^dead," treat it as 
though alive. It may be ^Hhro\Mi in" at any moment. 

Take no chances, protect yourself by short circuit- 
ing and grounding the line. 

Be very careful not to part wires, keeping one end 
in each hand ; you will cut yourself into the circuit. 

With old transformers especially, and with all trans- 
formers that are not grounded, treat the secondari^ 
as you would the primaries. 



CHAPTER XIV 

BATTERIES — PRIMARY BATTERIES 

The term, battery, is applied to a number of cells 
grouped together either in series or in parallel. It 
should never be applied to a single cell. Batteries may 
be grouped according to any of the methods shown in 




Figure 120 

Figure 120. For all ordinary work, the method at the 
top is employed. The voltage of this arrangement is 
four times as great as that of a single cell. 

If the same number of cells be grouped as in the 
center of the figure, the voltage will be but two times 

170 



Batteries 171 

that of one cell, but the current obtainable will be 
twice that of the above. With the arrangement at the 
bottom, the voltage will be equal to that of one cell, 
and the current obtainable four times as great as that 
from the first figure. The voltage of a number of cells 
in series is equal to the voltage of one cell multiplied 
by the number of cells. 

The voltage obtainable from any cell is independ- 
ent of its size or of the distance apart of the plates. 
In any given cell, however, the current obtainable is 
proportional to the size of the plates opposed to each 
other in the solution, and inversely as their distance 
apart. The distance apart of the plates affects the 
current only, as it increases the resistance. 

The fall of potential when current is flowing is pro- 
portional to the product of the resistance of the bat- 
tery or cell and the current in amperes. If the bat- 
tery has a high internal resistance therefor, the drop 
in voltage will be quite great when much current is 
taken from it. 

A battery is placed to the best advantage when the 
cells are so arranged that their resistance is nearest 
equal to that of the line through which they are work- 
ing. If the resistance of the line or instruments is 
greater than that of the battery all of the cells should 
be placed in series; if the external resistance is less 
than that of the battery, the cells should be arranged 
in multiple until their resistance becomes as low as 
that of the line. 

The resistance of a number of cells in series is equal 
to the resistance of one cell multiplied by the total 
number of cells. 



172 



Operating and Testing 



The resistance of a number of cells in parallel is 
equal to the total resistance of one of the series groups 
divided by the number of sets in parallel. 

Primary batteries are divided into two classes ; one 
of these is suitable for continuous work only, and will 
rapidly deteriorate unless kept at work. The other 
will very quickly run do^^n when kept in continuous 
use. 

The best known of the continuous current type is 
the ''gravity cell." In this cell the positive pole con- 




Figure 121 

sists of copper located at the bottom of the jar as 
shown in Figure 121, and the negative of zinc ar- 
ranged at the top, as shown. Both of the elements 
are immersed in a solution of sulphate of copper com- 
monly spoken of as ''blue stone.'' This type is suit- 
able only for such work as telegraphy, where very 
small currents are used. The internal resistance of 
this cell is very high. 

The open circuit batteries are far more in use and 
exist in many forms and include nearly all of the dif- 
ferent makes of dry batteries. Aside from dry bat- 



Batteries 173 

teries, the most notable kind is the Leclanche. In this 
cell the positive pole is of carbon immersed in a solu- 
tion of sal-ammoniac, and the negative pole is a piece 
of zinc immersed in the same liquid, but insulated 
from the carbon. This cell as well as the different 
kinds of dry batteries, are capable of delivering a 
strong current for a short time. If left in circuit, 
however, in a few minutes they will run down so that 
no current can be obtained. No matter, however, how 
badly such a cell may be run dowTi in time it wall 
often recuperate. These cells are universally used 
for bell and telephone work and consume no energy 
when not in use. 

If the following directions are carefully observed 
little trouble will be experienced. 

Leclanche and similar open circuit batteries. 

Use no more salomoniac than w^ill readily dissolve. 
Five or six ounces is the quantity required for ordi- 
nary cells. 

Do not fill jar more than three-fourths full of water 
and keep it in a cool place to prevent evaporation. 

See that water does not freeze. 

Remove such zincs as become coated wdth crystals. 
They are impure and introduce very high resistance 
in the circuit. 

Remove carbons and let them dry out occasionally. 

Do not allow battery to be in use very long at one 
time. 

Do not allow it to become short circuited. 

If battery has been short circuited disconnect it 
and it will often pick up again. 



174 Operating and Testing 

CLOSED CIRCUIT BATTERY — GRAVITY CELL 

Fill jar nearly full of water and throw in sufficient 
sulphate of copper (blue vitriol) to give a slight blue 
color to about half of the water. The blue part of the 
solution will be the heavier and will settle at the bot- 
tom. Enough should be provided so that the dividing 
line will be maintained about half way between the 
zinc and the copper. 

To start the action of this battery it may be short 
circuited for a while; it must never be left on open 
circuit for any great length of time. 

ACCUMULATORS OR STORAGE BATTERIES 

Storage batteries are used in connection with iso- 
lated or central stations, to supply current when the 
dynamos are not running, as well as at the hours of 
heaviest load when perhaps the capacity of the dy- 
namos may not be fully equal to the demands made 
upon them. 

It must be borne in mind that it is not customary 
to provide dynamo capacity for all of the lights and 
power connected to the system, the assumption being 
that seldom more than 25 to 50 per cent of the con- 
nected load will be used at any one time. If a suita- 
ble storage battery is connected to the system, the 
dynamo capacity may be even less, for the battery 
can be charged during the slack hours when but very 
little current is being used for other purposes. Thus, 
if properly arranged, the d}Tiamos and engines can 
be kept working at their full capacity and highest 
efficiency most of the time. 



Batteries 



175 



The plates of the cell are of lead (See Fig. 122) 
and there is always one more negative plate than 
there is of the positive. These plates are usually con- 
tained in glass or porcelain jars for the smaller sizes 
and for the larger portable batteries of hard rubber. 
The cells for very large permanent installations are 
often made up of heavy planking lined with lead. 

The positive plate always contains the ''formation 
which may be either mechanically applied, or 




Figure 122 

' 'formed" by the action of the charging current. 
Those batteries in which the active material is applied 
in the form of a paste are generally known as the 
Faure type, while those in which the active material 
is produced by charging and discharging are knowia 
as the Plante type. 

The electrolyte used in connection with these bat- 
teries is always sulphuric acid diluted to a specific 
gravity, averaging about 1.20. The acid should be 



176 Operating and Testing 

pure and the water used should be distilled. The 
battery room should be well ventilated and all iron 
work should be covered with water proof paint. 
Wooden floors should not be used. Cement floors are 
best. 

The cells should be well insulated and the specifi- 
cations of the National Electrical Code should be fol- 
lowed in this respect. 

The cells are connected with the positive pole of 
one to the negative of the other, just as an ordinary- 
battery, and they may also be connected in multiple. 
Connection in multiple, however, has no advantage 
that can not much better be obtained by procuring 
larger cells and is, therefore, very seldom practiced. 

The E.M.F. of a cell fully charged is about 21/2 
volts, and should not be carried much beyond this. 
When the cell is overcharged oxygen and hydrogen 
gas are given off. The E.M.F. should not be allowed 
to fall below 1.8 volts under any circumstances and 
the nearer at full charge the battery can be kept the 
better it is. On no account should any battery ever 
be left standing without charge, and the electrolyte 
should never be applied unless everything is in read- 
iness for immediate charging. 

The connections from one cell to another had better 
be soldered or welded so as to leave no chance for 
loose connection. 

As the water evaporates, it must be from time to 
time replenished. This is best done with a hose 
which may lead the water into the bottom of the jar 
where otherwise the heaviest part of the solution will 
concentrate. 



Batteries 177 

In handling water and acid, never pour water into 
acid; always ponr the acid into the water. Much 
heat is generated when the two are mixed. 

Every cell should be tested quite frequently with 
voltmeter and hydrometer. The best indications of 
the condition of a cell are obtained by hydrometer 
tests. 

If the voltage of one cell is much lower than that 
of the others, the cause will often be found to be a 
short circuit of some kind in the cell. 

To charge storage batteries it is necessary that the 
current pass into the battery in the opposite direc- 
tion that current flows from the battery when in use. 

In most cases it is necessary to charge the battery 
to a higher potential than that at which the dynamo 
operates. This cannot be done unless a *^ booster" of 
some kind is employed. A '^booster" is merely a 
generator through which the total current passing 
into the battery flows and in which a certain addition 
to the voltage of the circuit is made. 

Figure 123 shows the connections of a compound 
dynamo used to supply current to the bus bars, and 
also to charge a storage battery. In this figure B is a 
belt driven booster, through which all current pass- 
ing from the dynamo into the battery must pass and 
in which the pressure can be raised the desired 
amount. This booster is provided with fields like an 
ordinary dynamo, and the field strength can be ad- 
justed. To charge, the double throw switch S is 
thrown upward and current now passes from the plus 
pole of the dynamo to switch S, then along ware C to 
the main cells of the battery and through the battery 



178 



Operating and Testing 



ammeter, the booster the other pole of switch S and 
the minus pole of the dynamo. 

To discharge, the switch is thro\\TL downward and 
current now passes in the reverse direction to the bus 




Figure 123 

hars, leaving the booster out of circuit The discharge 
current, however, must pass through the cells con- 
nected at R. In the abo^^e case, these are simple lead 
plates knowTL as counter E.M.F. cells and oppose the 
flow of current so that by their aid the rate of dis- 



Batteries 



179 



charge can be controlled. As the battery discharges 
and its E.M.F. falls more and more of the cells are 
cut out. Very often the method of regulation is by 
means of end cells which are charged at the same tnne 
as the battery. In such a case the connections must 
be as indicated by dotted lines and wire C, as the 
E.M.F. of the battery falls, more and more of the end 
cells are cut into the circuit and their E.M.F. added 
to that of the battery 




Figure 124 



A method of arranging a storage battery so that it 
can be charged without the use of a booster is shown 
in Figure 124. This battery is arranged so it can be 
charged in parallel, and for this purpose is divided 
into two parts. When arranged for charge the two 
switches in the upper center are thro\\Ti downward 
and all of the end cells are cut into the circuit so they 
will be included in the charge. Current now passes 



180 Operating and Testing 

from the positive pole of the circuit through all of 
the resistance R, and the switch S to the two halves 
of the battery. As the counter E.M.F. of the bat- 
tery develops resistance is cut out of the circuit by 
closing the switches connected to the resistance, begin- 
ning at the right, one at a time and as fast as it ap- 
pears necessary. Closing the last of these switches 
at the left cuts out all resistance. Two ammeters are 
provided so the current in both sides can be watched. 

Ordinarily this battery ^^ floats" in the system and 
when arranged for work upper switch S is opened and 
lower switch S is closed. With this connection the bat- 
tery will feed into the line whenever the pressure of the 
line falls below the normal and take current from the 
line when the pressure is normal or above. Double 
scale ammeters should be used. They wall show 
w^hether the battery is receiving or sending current. 

When storage batteries are to be charged from al- 
ternating current lines, the Cooper-Hewitt Mercury 
Rectifier may be used. 

This mercury alternating current rectifier consists 
of a glass bulb fitted with four electrodes. Tw^o of 
these are of graphite and two of mercury. The mer- 
cury electrode will not allow a negative current to pass 
through into the vapor in the bulb, but does not resist 
the flow of current from a positive source into itself, 
if that current has been once established. In order 
to start the flow^ of current from the positive elec- 
trodes P into the mercury electrode N it is necessary 
to establish a metallic circuit from P to N and when 
now this circuit is interrupted the current will con- 
tinue to flow into the mercury from the vapor in the 



Batteries 



181 



bulb, so long as the current flow is not broken else- 
where. If for any reason the current flow ceases, it 
cannot again be started until the metallic circuit has 
again been established. 

The operation of the rectifier can perhaps be best 
understood by reference to the Figure 125. In this 



'CI 



roi)TmT'mi)WTWimT<m 




E^IR) 



Figure 125 



figure, A C is the source of the alternating current 
which is to be rectified for the purpose of charging 
the battery. The current passes from whichever side 
of A C may be positive to the positive electrodes P. 
So long as the bulb B remains in its upright povsition 
no current wdll flow from P into N. In order to start 
the flow it is necessary to tip the bulb a little to the 



182 



Gperating and Testing 



left so that the mercury in the bottom connects N and 
S. This starts current flow through the starting re- 
sistance R, and when the bulb is returned to the up- 
right position the current continues; but not from S 
but from P. No current can pass from the mercury 
to the vapor, but there is no hindrance to current flow 
from the vapor to the mercury, provided it has been 
started. As the arc lamp maintains itself through the 
vapor formed by the arc, so the current there main- 
tains itself when started through the vapor. Should, 
however, only for an instant the current flow be in- 



-O 



5 



-S|e ^ 



* 



L 



Figure 126 ^ 

terrupted the bulb would have to be tilted again. It 
will be seen from the figure that each side of the A C 
has an electrode at P, and one of these is always posi- 
tive and from whichever is positive the current flows 
into the mercury. 

A reactance E is cut into the circuit which causes 
the current to continue after the E.M.F. has fallen 
to zero until the current at the other side has attained 
some value so that the flow is continuous. 

Storage battery circuits are usually equipped with 
overload and underload circuit breakers, which pre- 



Batteries 



183 



vent charging at too great a rate and also a reversal 
of the battery current through the dynamo. 

Small batteries for use in connection with bell or 
telephone work are best connected for charging as 
shown in Figure 126, one battery being connected to 
the work while the other is charging. This makes it 
impossible to bring the high voltage dynamo current 
in contact with the bell wiring which, as a rule, is not 
safe for such pressures. The rate of charge can be 
governed by using more or less lamps of different c. p. 
in the sockets indicated at the right of the figure. 



■O 
O 
■O- 
O 
O 
O 



■O 
-O- 
O 
■O 
■O- 
O 



4 



itiiiiiiiti 



^f®t 




Figure 127 Figure 128 

Figures 127 and 128 illustrate other uses for stor- 
age batteries. These figures show the elementary 
connections of batteries used in a manner similar to 
compensators. It is here made possible by their use to 
obtain two voltages from one dynamo. 

There are so many different types of storage batter- 
ies and so many different sizes that it is impracticable 
to give detailed directions concerning their use. Di- 
rections pertaining to any particular battery had best 
be obtained from the maker. 



CHAPTER XV 

ARC LAMPS 

If we take t^YO suitable pieces of carbon and con- 
nect them to a source of electricity and then bring the 
ends together we shall, of course, obtain a current 
flow through them. If the contact between the two 
carbons is not very good, the current will make itself 
manifest by the heating of the small contact surface 
to redness. If we now slowly separate these points the 
current will continue to flow through the intervening 
air space, forming what is known as the electric or 
voltaic arc. AYhere the separation is small the cur- 
rent will be quite strong and a hissing or frying sound 
will be given out. An arc of this character is gener- 
ally spoken of as a low tension, or short arc and re- 
quires about 25 volts, and, for successful operation, 
very hard carbons. This type of arc is at the present 
time very little used for lighting purposes. 

If we continue to separate the carbon points the 
light becomes very unsteady and flickers considerably 
until at a certain point it begins to improve and we 
obtain the long, quiet arc. It will now be found that 
the carbons are separated about Vs of ^^ inch. By 
measuring the difference of potential across this arc 
we shall find from about 45 to 50 volts and this is the 

184 ■ 



Arc Lamps 185 

proper voltage for open arcs. If we continue to in- 
crease the separation of the carbons, the arc will grow 
longer and become decidedly flaming until finally the 
separation becomes too great and the arc breaks. 

The resistance of the arc is very nearly proportional 
to the cross section of the carbons and increases with 
an increased separation of the carbon points. The 
drop in voltage across the arc is not entirely propor- 
tional to this resistance, but is also due to a peculiar- 
ity of the arc which causes it to act as though a coun- 
ter E.M.F. was set up in it. 

The temperature of the arc is very high, about 3500"^ 
Centigrade, and there is nothing that can withstand 
it. By its help we can drill through the hardest steel 
or rock or the most effective insulation with equal 
ease so that, so far, it has been found impossible to 
construct an^^thing that can resist it. 

The light of a strong arc is very injurious to the 
eyes and has often caused considerable distress and 
even temporary blindness. This is especially the case 
where an arc of two or three hundred amperes is used, 
as for instance, in the drilling of iron beams, or in 
electric furnaces Avhere upward of 10,000 amperes are 
sometimes used. Under all circumstances it is best 
to view the arc through darkened glasses, although 
the ordinary ten ampere arc will not injure the eye 
unless it is exposed to the light very long. 

The length of the arc, or the space between the. car- 
bons, varies from 1/32 of an inch to one inch After 
a lamp has burned for some time, the carbons will be 
found to have assumed the shape shown in Figure 
329. It will be noticed that the upper, or positive, 



186 Operating and Testing 

carbon has been burned in the form of a crater while 
the lower carbon has been burned to a point. The 
crater formed in the upper carbon acts as a reflector 
and it is from this point that the greatest amount of 
light, or about 80 per cent of the total light of the arc, 
is emitted For this reason the positive carbon always 
occupies the upper position unless, for special rea- 
sons, it is desired to throw the greater proportion of 
the light in an upward direction. It will also be found 
that the positive carbon burns away about twice as 
rapidly as the negative carbon. The rapid consump- 




Figure 129 ^ 

tion of the upper carbon is due to the vblatilization 
of the carbon at the crater, considerable vapor being 
formed at this point which is carried across the arc 
and condensed on the negative carbon. 

If, when the arc lamp is burning in its normal con- 
dition, the carbons are separated, it will be found that 
the upper carbon is heated for a greater distance back 
from the point than the negative carbon, and it will 
take longer to cool off. This fact, and the nature of 
the shadows cast, forms an easy and practical method 
of determining whether or not, to use the language 
of the lamp trimmer, the arc is burning right or is 



Arc Lamps 187 

burning ^^ upside do^\TL." When the arc is burning 
with a long separation of the carbon points, the cra- 
ter almost wholly disappears and the carbons become 
rounded off. 

When arc lamps are used on alternating current cir- 
cuits a voltage of about 28 is used and the current 
must be correspondingly increased. Each carbon be- 
comes alternately positive and negative and the two 
carbons burn to points and are consumed at about 
the same rate, the difference in consumption between 
the upper and lower carbon being due to the fact that 
the heat from the lower carbon rises and increases the 
carbon consumption of the upper carbon slightly. The 
alternating current are is much noisier than the direct 
current arc for all ordinary frequencies, but with 
very high frequencies this noise ceases. Many lamps 
cannot be operated on low frequencies such as 25 cy- 
cles per second. It is not practicable to operate any 
of them much below 25 cycles, as the interval during 
which the current practically ceases becomes of such 
length that the vapor between the carbon points cools 
off sufficiently to entirely interrupt the current. 

Any arc light is affected by strong drafts of air. 
This will often literally blow out the arc and cause 
rapid feeding and short arcs which in turn bring about 
very rapid consumption of the carbons. A magnet 
applied to the arc also has the effect of blowing it out 
and this fact is often made use of in lightning arrest- 
ers and in connection with some arc machines where 
the commutator design is such that severe sparking 
ensues. 

While some of the light of the arc is emitted from 



188 Operating and Testmg 

the arc itself, it is, especially in open arcs, but a very- 
small proportion of the total light. Most of the light 
is given out from the carbon points and the quality 
of the carbon therefore has a great influence on the 
character of the light If a poor carbon is used, the 
arc rotates about the carbon, this effect being more 
noticeable when large carbons are used. Impurities 
in the carbon will also cause the arc to constantly 
vary its position and more or less spluttering will oc- 
cur, accompanied by a constant change in the color 
of the light. 

As a rule, the best carbon is the one that has the 
greatest range from the point of hissing to the point 
of flaming. With any given carbon these two points 
vary with the length of the arc. If the arc runs too 
short we have the hissing sound, when the arc runs 
too long it is the flaming that annoys us. It is evi- 
dent that if carbons can be found to burn without 
hissing or flaming over a long range, we need not 
be near so careful with the adjustment of the lamp. 
As this long range of carbons varies also w^ith their 
purity, the test for range is also a good test for the 
light giving qualities of the carbon. As a rule, the 
greater the range of any carbon the more serviceable 
it is. 

The test for range as usually carried out is made in 
the following manner : Insert the carbons to be tested 
in a hand feed lamp. Let them bum with a normal 
current until they have established the proper points. 
Now feed them together slowly until the hissing point 
is reached, and note the voltage across the arc (not 
the whole lamp). Next, separate the carbons slowly 



Arc Lamps 189 

■until they begin to flame, and note this voltage. As 
has been stated before, the greater the range of volt- 
age through which the carbons can be operated, the 
better they are. The hissing point is usually about 42 
volts, and the flaming point about 62 volts. 

To test the comparative life of carbons, it is neces- 
sary to observe the quantity consumed by a given 
current and voltage in a given time. This is best done 
by arranging that the same current, at the same volt- 
age, shall pass through each arc lamp. Then by weigh- 
ing, before and after burning, the exact amount of 
carbon consumed in a given time can be ascertained 
The approximate useful life of a carbon can be easily 
determined by burning it for a stated time and ob- 
serving the amount consumed. The length of the car- 
bon available for burning (not the whole carbon), 
divided by the length consumed in a given time will 
give the approximate life of the carbon. 

The resistance of carbons is of importance in two 
w^ays: first, it consumes energy and, second, some of 
the forced, high-resistance carbons do not easily strike 
an arc, i. e., do not volatilize readily enough. The re- 
sistance may be measured either w^ith a Wheat- 
stone bridge or with a voltmeter as explained in the 
chapter on testing. In order to reduce the resistance 
of the carbons, they are sometimes coated with copper. 
This will also prolong their life somew^hat. Copper 
coated carbons are more generally used for outside 
lighting and should never be used on inside lamps 
unless the arc is entirely enclosed, as hot pieces of cop- 
per are thrown off. Another method of reducing the 
resistance of the carbons is to provide a wire or strip 



190 Operating and Testing 

of metal running through the length of the carbon 
rod. This scheme is made use of in the flaming arcs 
where long carbons of small cross section are used. 

Cored carbons can be burned at a lower voltage 
and, if used in conjunction with solid negative car- 
bons will, on direct current, give a very steady arc. 
The soft core being in the center of the carbon allows 
that part of the carbon to burn away faster and thus 
maintain the crater and the arc in one position. Metal 
electrodes are used in some forms of lamps, various 
advantages being claimed for them. They always form 
the negative electrode for, if used on the positive side 
they are very rapidly consumed. 

While there is no definite relation between the size 
of the carbon and the current, it is evident that there 
are conditions which must limit us from either ex- 
treme. If a small carbon were used with a large cur- 
rent, considerable hissing would result, and the carbon 
would be rapidly consumed, while with a large carbon 
and a small current the arc would rotate around the 
carbon and the light would be very unsteady. The 
carbon points would not be heated to any great extent 
and the efficiency would be low. The size of the car- 
bon rods and an outline of the general practice is given 
in the following table : 



Arc Lamps 



191 



ENCLOSED ARC 


Volts 


Amp. 

5 
3 


Upper 


Lower 


75-80 
to 
80 


12 in, xi in. 
12 in. X I in. 


^ in. X ^ in. 
6 in. X i in 




OPEN ARC 


Volts 


Amp. 


Upper 


Lower 


45 
to 

50 


9.0 
6.8 


llin. xfin. 
12 in. X /gin. 


Sin. x|in. 
7 in. X ^^s '"• 




HAND FEED 


Volts 


Amp. 


Upper. 


LoM-er 


45 
to 
50 


5-10 
25-vO 


6 in. x /e in. 
6 in. X i in. 


6 in. X x's ii^' 
6 in. X f in. 



Arc lamps are generally rated according to candle 
power. This is a very much abused and misunder- 
stood method of rating. It is evident from an exami- 
nation of Figure 130 that the candlepower of the arc 
will depend upon the position from which the meas- 
urement of the candlepower is made. Figure 130 
will give a general idea of the manner in which this 
candlepower varies in the case of the ordinary direct 
current arc. The greatest amount of light is given 
out at an angle of about 45° with the horizon. Di- 
rectly above and below the lamp the candlepower is 
practically nothing, for, in these positions, shadows 
are cast by the lamp frame. The relative candlepow^- 
ers at other positions are shown by the length of the 
radial lines from the center to the curve in the figure. 

With alternating current arcs the carbons are al- 



192 



Operating and Testing 



ternately positive and negative, and the distribution 
of light is somewhat different from that of the direct 
current lamp. The maximum candlepower for an arc 
consuming the same amount of current is less with 
an alternating current than with a direct current and 



aoloo 




Figure 130 



the maximum light is thrown out at different angles. 
Figure 131 shows the distribution of light from an 
open, alternating current arc. It will be seen that 
there are two points of maximum candlepower, one at 
40° below the horizontal and the other at 40 "^ above 
the horizontal. 



Arc Lamps 



193 



It is evident from the foregoing description that, 
to compare the light given out by arc lamps it would 
be necessary to take into consideration the light given 
out at all angles above and below the horizontal. This 
is known as the mean spherical candlepower, and is 
obtained by taking candlepower readings around the 
half circle as shown in Figure 130 or Figure 131, and 
taking the mean. This is given as about one-third the 




Figure 131 

maximum candlepower. For a lamp with a maximum 
candlepower of 2,000, the mean spherical candlepower 
would be about 660. The accurate determination of 
the mean spherical candlepower is a rather difficult 
procedure and requires the use of special apparatus. 
A better method of rating arc lamps now in gen- 
eral use is the wattage rating. The average wattage 
rating of the various standard lamps is a^ follows : 



194 



Operatiiig and Testing 



9.6 amps., 50 volts, 2000 nominal c. p., 480 watts. 

6.8 amps., 50 volts, 1200 nominal c. p., 340 watts. 

The proper placing of arc lamps for a given illumi- 
nation will depend upon the amount of light required. 
According to many authorities, an expenditure of i^ 
watt per square foot will give medium illumination 
such as is used in train sheds while the most brilliant 
illumination called for can be obtained with 2 watt-s 
per square foot. This corresponds to approximately 
the distances apart as given in the following table : 

TABLE B 



Medium Illumination 


, 


Brilliant Illumination 


Distance 
Apart 


Height 


Distance 
Apart 


Height 


22 feet I 10 to 15 feet 
30 feet 1 15 to 20 feet 


(3 amp. enclosed arcs.) 12 feet 10 feet 

(6 amp. enclosed arcs.) 1 21 feet 12 to 15 feet 



The higher lamps are hung, the evener will be the illumination. 

As a general rule, it is accepted that the distance 
apart of arc lamps should not be greater than six 
times their height above the floor. Actual practice, 
however, in many instances varies widely from this 
and often the distance apart is 10 or 15 times the 
heigrbt of the lamp, while in other cases only two or 
three times the height is taken as the distance apart. 

AYith a direct current arc lamp the maximum light 
is given out at ^-n angle of 45° below the horizontal 
and very little light ir- ^s-iven out in an upward direc- 
tion. It is evident that a -circular area at a distance 
from the pole equal to the height of the lamp will be 
very brightly illuminated, and, as we move away from 
this position the illumination rapidly diminishes. The 
alternating current arc gives a different distribution 
of light, the maximum amount of light being given 



Arc Lamps 



195 



out at angles of 40° above and below the horizontal. 
By the u^e of properly designed reflectors, the light 
which is given off in an upward direction may be so 
reflected as to greatly increase the illumination over 
an extended area and at the same time the bright band 
of light close to the lamp which is present in the case 




©o- 



ao 



Figure 132 

of a direct current lamp is done away with. (See 
Figure 132.) It is in a measure due to this better 
distribution of light that the alternating current has 
come into such general use. 

In order to start any arc lamp it is necessary first 
to bring the carbons together, so that the current can 



196 Operating and Testing 

flow through them and then to separate them to a 
fixed distance so that the current will be forced to flow 
through the space separating the carbons and thus 
produce the arc. There are two general conditions 
under which this action may take place; one is that 
of a large number of lamps connected in series, the 
same current passing through each and the voltage 
being increased or decreased in proportion as the num- 
ber of lamps is increased or decreased. The other is 
that of a single lamp being independently placed in 
circuit in multiple with other lamps or whatever other 
devices there may be connected. In the flrst case each 
lamp must be equipped with means whereby, should 
its carbons be burned out or the lamp mechanism oth- 
erwise deranged so that current does not flow through 
the carbons, the current will be automatically shunted 
around this lamp and continue to feed the balance of 
the lamps in the circuit, so that only the lamp that is 
out of order will be left dark. 

With the other type of lamp this device is not nec- 
essary, because the lamp burns independently of all 
others and whenever it is out of order there are no 
other lamps dependent on this circuit for current. As, 
however, when the carbons are brought in contact the 
resistance of the lamp circuit is very low, there is 
likely to be an enormous rush of current through the 
lamp unless some means of checking it is provided. 
For this reason every lamp working on an independ- 
ent circuit must be provided with a resistance cut in 
series with it which will keep the current from becom- 
ing too g^eat while the lamp feeds or the carbons re- 
main together. 



Arc Lamps 197 

In connection with alternating current lamps the 
same observations apply with the difference that here, 
instead of a resistance, a reactance is used. The 
magnet cores are always laminated to reduce the loss 
and heat due to foucault currents. 

The open arc lamp has a number of objectionable 
features which are causing it to rapidly pass out of 
use. Owing to the fact that the arc is open this type 
of lamp is more or less of a hazard when used in prox- 
imity to inflammable material. Sparks of hot carbon 
are thrown off and, if copper coated carbons are used, 
hot copper is also thrown off. If the lamp is used for 
inside lighting, such as in a store, for instance, it is 
absolutely essential that some form of spark arrester 
be provided. An open arc operates satisfactorily only 
at from 45 to 50 volts, so that if it is desired to use a 
lamp of this kind on a 110-volt circuit, a resistance 
must be provided to reduce the voltage to this amount. 
This resistance will, of course, consume as much or 
more energy than the lamp itself, this energy being 
practically wasted. AVhile two lamps could be oper- 
ated in series on a 110-volt circuit, this method has not 
given the satisfaction desired. The open arc must 
be trimmed, or provided with new carbons, about ev- 
ery 8 to 16 hours, depending on the style of lamp 
used, and, if the arc is exposed to the weather, they 
are more or less affected by the wind, a strong wind 
often blowing the arc out. 

All of these objectionable features are overcome in 
the ''enclosed" arc where the carbons, or that part 
of them in the vicinity of the arc, are completely en- 
closed in a glass globe. Figure 133 shows the ordi- 



198 



Operating and Testing 



nary method of enclosing the arc and, while there are 
many variations in detail both of the enclosing globe 
and the cap at the top, the principle of all of them is 
the same. The glass globe G either sets on an air tight 
base, or is entirely closed at the bottom The top of 
the globe is closed by a cap which is provided in the 
center with an opening through which the upper 




Figure 133 

carbon descends. This cap is generally arranged to 
allow of some play sideways so that the carbon will 
not bind, should it be of slightly irregular shape, and 
the joints between the cap and the globe are ground 
smooth so as to exclude the air as much as possible. 

When an arc is started in an enclosure of this kind 
whatever oxygen is present in the inside of the globe 
is soon consumed and the arc will then be surrounded 



Arc Lamps 



199 



by a carbon gas. The absence of oxygen greatly les- 
sens the consumption of carbon, and, with one trim- 
ming, the lamp will bnrn 100 to 150 hours depending 
on the size and length of carbon used. The presence 
of this gas also allows of the use of a higher voltage 
across the arc w4th a corresponding reduction in the 
current strength. A steadier light is also obtained. 

Another peculiarity of the enclosed arc will be no- 
ticed in Figure 133, where it will be seen that the 
carbons do not burn to points but remain somewhat 




Figure 134 

flattened. This results in a better distribution of the 
light. The enclosed arc requires a voltage of from 72 
to 80 volts at the arc, the carbons being separated 
about % of an inch, and is, therefore, much better 
suited for operation in multiple on 110 volt circuits. 
The arc being completely enclosed, makes the lamp 
safe for operation in most any location. 

The general principles upon which arc lamps are 
constructed will be explained in connection with the 
following figures: 



200 Operating and Testing 

Figure 134 shows in simplified form the circuits of 
the ordinary differential arc lamp. The series coil 
M (shown by the heavy lines), is connected directly 
in series with the carbons, while the shunt coil A 
(sho^TL by the light lines) is connected in shunt 
around the arc. These coils are so wound and con- 
nected that, when energized, they attract the core S 
in opposite directions, the series coil M tending to 
draw it down and the shunt coil A up. The move- 
ment of the core depends upon the difference between 
the attraction of the two coils, therefore it is known 
as the ^'differential'' winding. Any movement of 
the core S is communicated by means of the lever arm 
to the upper carbon. 

Normally, in this form of lamp, the carbons are in 
contact when the lamp is not burning. The operation 
of the lamp is as follows: Current entering at the 
positive binding post P has two paths by means of 
which it may get to the negative binding post N. One 
of these paths is through the high resistance winding 
A, and the other through the low resistance offered 
by the series coil M and the two carbons which are in 
contact. It is evident that the current will take the 
easier path through the coil M and this coil will then 
become energized and the core S will be dra^^Ti down- 
ward, the upper carbon at the same time being raised, 
separating the carbon points and producing the arc. 
As soon as the arc is formed more or less resistance, in- 
creasing with the length of the arc, is introduced into 
the circuit of the series coil and some current will 
now flow through the shunt coil A, energizing this 
coil and attracting the core S in an upward direction. 



Arc Lamps 201 

Obviously a point will soon be reached where the at- 
traction of the two coils is equalized and the upper 
carbon will come to rest. 

As the upper carbon burns away, and the length of 
the arc increases, the current through the series coil 
becomes gradually weaker and that in the shunt coil 
stronger, with the result that the core is drawn up- 
ward and the carbon points approach each other until 
a balance is again obtained. The mechanism through 
which the movement of the carbons is effected and 
the manner of connecting the various circuits differs 
in the several makes of lamps. Of these methods the 
following are in more common use. 

In some lamps the carbons are carried by a train 
of clock gears, and this gearing is under control of 
the two magnets, operating somewhat in the manner 
described. In other forms of lamps the series magnet 
lifts the carbons direct and the office of the shunt mag- 
net is simply to close a short circuit around the lifting 
magnet and thus to deenergize it so that the carbons 
may feed. This operation is sometimes reversed, the 
series magnet being short-circuited after the arc has 
been produced and the movement of the carbon ef- 
fected by the shunt magnet. In still another style of 
lamp a small reversible motor is connected to the 
carbons in such a manner that it may either bring 
them together or separate them. The motor is pro- 
vided with two field windings, which oppose each 
other, and whichever is the stronger determines the 
direction in which the motor revolves. In connection 
with any of these plans it is possible to arrange so 
that the carbons may be either together or separated 



202 



Operating and Testing 



when the lamp is at rest. In the first case the first 
impulse of current separates the carbons, and in the 
other it must draw them together to start the arc. 

The diagram of the connections of a lamp designed 
to burn on a series circuit with many others is sho\vn 
in Figure 135. This lamp has the same differential 
winding as that previously described and in additon 
is provided with an automatic cut-out, C. It will be. 




Figure 135 



noticed that the magnet winding of this cut-out is in 
circuit with the shunt coil and the current through it, 
therefore, increases as the arc grows longer. If the 
carbons fail to feed, or if the arc grows very long, 
and in consequence is extinguished, the current flow- 
ing through this magnet winding becomes strong 
enough to cause the armature A to be raised and the 
circuit at E is closed. The main current now passes 



Arc Lamps 



203 



from P, through R, to the armature A, point E, and 
to the negative terminal N. Thus the current is 
shunted around the lamp and all other lamps in the 
circuit are left burning as before. The purpose of R 
is to maintain some current in the shunt coil. This 
often starts the lamp again. This style of lamp is 
never extinguished by opening the circuit, but always 
by closing a short circuit around the lamp. 




Figure 136 



With arc lamps for use on series circuits it is essen- 
tial for the successful operation of the lamp that both 
a shunt and series coil be provided. For lamps to be 
used on multiple circuits, or circuits where the voltage 
is constant, and where the current flow depends only 
on the resistance, the lamp will work successfully with 
either a shunt or series winding. Both windings are 
not necessary. 

Figure 136 shows a type of lamp which is operated 
with a series winding only. In this case the current 



204 



Operating a7id Testing 



strength varies with the distance apart of the carbons. 
When the current becomes stronger the magnets be- 
come more powerful and draw up the upper carbon, 
increasing the separation between the carbon points. 
As the current weakens, the carbons come closer to- 
gether. This lamp is placed singly in circuit and is 




Figure 137 

often used on alternating current circuits. E is a 
reactance which with alternating currents takes the 
place of the resistance used with direct currents and 
prevents excessive rise of the current strength when 
the lamp is started. It is evident that a lamp of this 
type could not be used on a series, constant current 



Ajx Lamps 205 

circuit, for the current flowing through the series 
coil would never alter and w^ould not be affected by 
the separation of the carbons. While a lamp con- 
trolled only by a shunt coil would operate on either a 
series or a multiple circuit their use on series circuits 
is not satisfactory, for when starting the carbons must 
be separated and the shunt coils of all the lamps are 
then thrown m series, this necessitating a considerable 
voltage to start them. 

Figure 137 shows the circuits of the flaming arc 
lamp. In this lamp carbons, the cores of which con- 
sist of certain chemicals which give to the arc the pe- 
culiar color, are used. A much longer carbon is neces- 
sary^ with this form of lamp and the carbons are of 
small diameter. The operation of the lamp is as fol- 
lows : AYhen the lamp is not burning the carbons are 
separated and no current can pass through them until 
the shunt magnet S has become energized and pulls 
over the arm A. As it does so the lever L (by means 
of mechanism not shown) drawls the carbons together 
and this allows current to flow through them. A very 
strong current now passes through the series magnet 
B, drawing the arm A away from the shunt magnet S. 
This action causes the carbons to be separated and 
establishes the arc. The resistance of the arc lessens 
the current flow and consequently weakens the series 
magnet so that the shunt magnet again comes into ac- 
tion and partially drawls the arm A aw^ay from the 
series magnet In this manner a point is soon found 
at which the arm comes to rest between the two mag- 
nets. As the arc bums away the shunt magnet be- 
comes stronger and the series magnet weaker and in 



206 Operating and 'Testing 

consequence the carbons are brought closer together, 
i. e., the lamp feeds. 

When the carbons have been fully consumed, the 
small chain shown at the right is drawn down to its 
limit and opens the shunt magnet circuit at C. This 
gives the series magnet full control over the arm A 
and it is drawn all the w^ay over, thus separating the 
carbons and extinguishing the arc. 

The magnet M answers a double purpose. The se- 
ries winding causes a slight magnetization which tends 
to force the arc downward away from the economizer 
E. So long as current passes through the winding of 
the shunt magnet S the small spring carrying contact 
is held down and the fine wire circuit around magnet 
M is open. "When, however, the shunt magnet circuit 
is opened, as by the stretching of the chain, the spring 
closes the circuit and this causes a strong magnetiza- 
tion to be set up in M which completely extinguishes 
the arc. This fine wire winding is used only w^here 
the arc is operated at high pressure and is not needed 
on 110 volt circuits. 

The operation of this lamp on alternating current 
circuits is somewhat different from that just described. 
The carbons rest in contact when the lamp is not 
burning and, instead of being controlled by the arm 
A, a small rotor which is under the influence of two 
opposing magnets is employed. When current is 
turned on the series magnet controls the rotor and 
causes it to raise the carbons and strike the arc. When 
the arc is started the shunt magnet increases in 
strength and causes the rotor to slow do\^Ti. As the 
length of the arc continues to increase the shunt field 



Arc Lamps 207 

becomes strong enough to finally reverse the rotor and 
feed the carbons together. The method of opening 
the circuit when the carbons are burned out is about 
the same as with the direct current lamp. There is 
no fine wire winding on the blow-out magnet. 

OPERATION 

The proper care and management of arc lamps re- 
quires first of all, that the operator be thoroughly fa- 
miliar with the principles of operation and all the de- 
tails of construction of the lamps under his care. It 
is well, therefore, for the operator to begin by remov- 
ing the jacket and carefully examine all parts of the 
lamp so as to thoroughly grasp the purpose and man- 
ner of operation of each part. It is also of advantage, 
if one can safely do so, to watch the operation of the 
lamp while it is burning. 

Lamps are usually trimmed in the following man- 
ner : Lower the lamp ; remove globe ; take out lower 
carbon; let dowTi upper carbon rod and thoroughly 
clean it with crocus cloth. The successful operation 
of the lamp depends to a great extent on the condi- 
tion of this rod. It must be clean, so that the clutch 
will firmly grip it. It must not, by any means, be 
greasy. If the rod becomes dirty it will soon be pitted 
by the current which passes to it from the contacts in- 
side the lamp and pitting once started rapidly in- 
creases. Remove upper carbon and place it in the 
lower holder. The length of the lower carbon should 
be measured. A handy manner of doing this is to 
prepare a gauge of proper length or file a notch in the 
pliers at the proper point. If the lower carbon is 



208 Operating and Testing 

either too long or too short and the lamp is burned un- 
til the upper carbon is entirely consumed, one of the 
carbon holders will be burned. Place upper carbon 
in position and align it with the lower by turning it 
freely about to see that it centers in all positions ; 
raise and lower the upper carbon several times to see 
that it works freely; clean and replace the globe and 
raise lamp to its normal position. If circuit is alive 
test lamp to see that it burns. 

It is possible for a good trimmer to take care of 100 
or more arc lamps per day, if they are close together. 
Where they are far apart and conditions are more dif- 
ficult, 50 lamps will be sufficient. 

If the lamp is of the enclosed type, where the lamp 
clutch feeds the carbon direct, it is necessary to ex- 
amine the upper carbon to see that it is straight and 
smooth. Any burs or projections should be removed 
and the carbon should be raised and lowered to see 
that it moves freely through the clutch and gas cap. 

The care of globes is also of great importance where 
enclosed arcs are used. Impurities in the carbon are 
thrown off in the form of a powder, and if this is not 
removed the useful light of the lamp will be greatly 
reduced. It is good practice to occasionally return the 
globe to the shop where they can be thoroughly 
cleaned. The gas cap must also receive careful atten- 
tion, for if this does not fit tightly, the operation of 
the lamp will not be satisfactory. 

The following are the principle points to be ob- 
served in the handling of arc lamps : 

Be sure that the voltage is right for lamps connected 



Arc Lamps 209 

in multiple and the current for lamps connected in 
series. 

Never switch a multiple lamp by shunting the cur- 
rent around it ; always open the circuit. 

Never open the circuit of a series lamp; always 
shunt the current around them. 

Never try to burn a multiple lamp without an 
additional resistance in the circuit. 

Never place a resistance in the circuit of a series 
lamp. 

Never handle high tension lamps without insulating 
yourself from the ground. 

It is inadvisable to touch the wires on opposite sides 
of the lamp at the same time. To be safe in this respect 
confine yourself to working with one hand at a time. 

Keep all parts of the lamp clean, especially the rod 
and the globe. 

Provide spark arresters for all open arc lamps 
where there is inflammable material. 

Never leave a lamp without globes where the wind 
can strike it. The arc will be continually blown out 
and consume carbons very fast. 

If an arc casts shadows or throws considerable light 
upward, it is an indication that it is burning upside 
down. To make sure that the lamp is burning upside 
down, separate the carbons; the one that is red far- 
ther from the point is the positive. 

A green light coming from the lamp indicates that 
the carbon holders are being consumed. This will 
generally occur if the lamp is left burning upside 
down for a considerable length of time, or if the car- 
bons are not of the proper length. 



210 Operating and Testing 

TESTING 

For the testing of an arc lamp practically all that 
is needed is a reliable voltmeter and ammeter, if se- 
ries lamps are being tested, it is essential that the ma- 
chine furnishing current to the testing circuit be in 
good condition and regulated properly. If a multi- 
ple lamp is being tested the voltage of the supply cir- 
cuit should be constant. The lamp should be located 
away from draughts of air and with series arcs special 
precautions must be taken to see that the place upon 
which the operator stands is well insulated and that 
under no circumstances can contact be made with the 
lamp and a ground at the same time. This is of great 
importance where tests are made on a regular circuit 
which is in use. 

Current and voltage tests can be made and the lamp 
accurately adjusted to the current and voltage for 
which it is designed. Detailed instructions are gener- 
ally given by the manufacturers for the adjustment 
of each particular type of lamp. These adjustments 
are generally obtained by altering the connections on 
the variable resistance or by changing the tension on 
the springs. Voltage readings should be taken as the 
lamp feeds and the cut-out if a series lamp, should 
also be tested to see that the lamp cuts out at the 
proper voltage. This test is made by slowly separat- 
ing the carbons until the arc breaks. One of the most 
common causes of trouble will be found in the cut-out 
and this should be thoroughly cleaned and tested. A 
defective cut-out generally results in burned out coils. 



Arc Lamps 



211 



SERIES ARC SWITCHBOARDS 

The switching of series arc light circuits is a prob- 
lem altogether different from any other. At the pres- 
ent time, very few new systems of this kind are in- 
stalled, but there are still quite a number of old in- 
stallations that must be reckoned with. 

Figure 138 shows diagrammatically the well known 
Thomson-Houston switchboard. In this system there 




Ov^ 



Figure 138 



are two horizontal rows of holes, one at the right and 
one at the left for each machine. There are also tw^o 
vertical bars containing holes for each circuit on the 
board. The board may be built for any number of 
circuits or machines. The low^er row^ of holes is extra 
and is provided to facilitate connecting several or all 
of the machines or circuits in series. 

The machines arc connected to the circuits by means 



212 Operating and Testing 

of plugs which pass through from the front of the 
board and connect the horizontal bars to the vertical 
at whatever point a plug may be inserted. If a plug 
be inserted where the positive side of machine A con- 
nects to circuit 1 and another where circuit 1 feeds 
into the negative side of the same circuit, machine A 
wdll be in position to operate this circuit. The position 
of plugs is indicated by the black circles and by trac- 
ing out the circuits it will be seen that machine B is 
supplying circuits 2 and 3. All of the positive leads 
of the machines go to one side of the board and the 
positives of the circuit must be connected to the same 
side. Whenever it is desired to run several circuits 
from one machine the negative of the first circuit must 
be connected to the positive of the next. 

If circuit 3 is to be disconnected from machine B, 
insert plug where circuit 2 crosses bar of machine B, 
at the right of board. This w^ill put out the light of 
3 and the plugs may now be withdrawn. 

Another style of switchboard for the same purpose 
is shown in Figure 139. Here the connections from 
machine to circuit and from circuit to circuit are 
made by flexible cables, which carry suitable plugs at 
each end. In this diagram machine A is supplying 
circuit 1 and machine B circuits 3 and 4. Three holes 
are provided at the terminals of each circuit and 
machine to allow of the use of auxiliary plugs in 
switching. If circuit 2 is to be added to machine A, 
auxiliary plugs are used as shown by dotted lines. 
The main cable C from minus side of circuit 1 may 
now be withdrawn. This will force current through 
circuit 2 and the permanent plugs may now be placed 



Arc Lamps 



213 



in the center of the holes. If circuit 2 should contain 
many lights or be open, a long flash would accompany 
the withdrawal of the plug. 

To disconnect circuit 3 from machine B insert aux- 
iliary plug, as indicated by broken line and withdraw 
cables D and E. 

When it is desired to dispense with one of the ma- 
chines and let the other do all of the work, the trans- 
fer can be made without disturbing the lights by first 




Figure 139 



connecting the two machines in series on all of the 
circuits in use. When this is done, short circuit the 
fields of the machine A that is to be cut out, and then 
short circuit the whole machine and disconnect it. 

Switching arc circuits is somewhat confusing to one 
who is not familiar with it, and it is advisable for any 
beginner to study out the best methods for the par- 
ticular board with which he has to work. He should 



214 



Operating and Testing 



have the whole system in his head so as to avoid the 
necessity of studying over the problem when circuits 
are to be changed in a hurry. 



^/ 



v/ 




Figure 140 

Figures 140 and 141 show methods of controlling 
alternating current arcs operating in series. In Fig- 




•N 



Figure 141 

Tire 140 the weight W balances the two cores of the 
coils M. When a current passes through these coils 
they draw in the cores and in so doing increase the 



Arc Lamps 



215 



reactance of the circuit. This in turn cuts down the 
current. In the above manner the device automatic- 
ally regulates the current and keeps it very close to 
its predetermined value. This device is used only for 
constant current arc lamps. 

A somewhat different principle is employed in Fig- 
ure 141. In this figure P is the primary coil of a 
series transformer and the current from the gen- 



r\ 



cnnr) 













Figure 142 



erator always passes through it. This current induces 
secondary currents in the coil S. This coil is balanced 
by the weights AV, and is free to move up or down. 
If the current in the secondary increases beyond a 
predetermined amount, the repulsion between the two 
coils is increased and the upper one rises. This les- 
sens the induction and cuts down the current. If the 
current becomes weak, the operation is reversed. 



216 Operating and Testing 

Where it is desired to use direct current arc lamps 
from alternating current circuits, the Cooper-Hewitt 
Mercury Eectifier is often used. A diagram of the 
connections of this device is shown in Figure 142. The 
principle upon which this is based is outlined in an- 
other chapter and need not be repeated here. It is 
w^ell known that the current can pass from the posi- 
tive electrodes P into the negative or mercury elec- 
trodes N when once established, but cannot pass from 
the negative electrode to the positive. 

In order to start the operation, the glass bulb is 
tilted a little so that the mercury of the two lower 
electrodes unites ; this starts current from the starting 
transformer S and when the bulb is returned to its 
normal position the current breaks, causing an arc. 
This allows current from whichever of the upper elec- 
trodes is positive at the time, to pass into the negative 
and feed the arc lamps. As the polarity of the upper 
electrodes unites ; this starts current from the starting 
negative ceases and that from the one that is now 
positive begins. 

A reactance which will cause the current from the 
first pole to overlap that of the succeeding one must 
be provided, or the current will cease entirely should 
it ever go to zero. 



CHAPTER XVI 

INCANDESCENT LAMPS 

For the illumination of small spaces such as offices, 
residences, etc., the incandescent lamp is without doubt 
the most useful and economical. This is principally 
due to the even distribution of light which the small 
units make possible, and to the readiness with which 
the lamps may be adapted to numerous lighting 
schemes. 

Originally all commercial incandescent lamps were 
made with carbon filaments, but within the last few 
years new types of filaments have been developed and 
these are, to a great extent, replacing the carbon fila- 
ment. 

In the carbon filament lamp a filament or thread is 
formed of some material rich in carbon, fibers of 
bamboo being originally used for this purpose. At 
the present time practically all carbon filaments are 
made by forcing a cellulose compound through suita- 
ble dies, the filament being hardened, cut to the proper 
length and placed on forms. It is then entirely sur- 
rounded by carbon in some form, so as to exclude all 
air and heated for several hours in a furnace. 

After it is cooled the filament is removed from the 
form and connected to the leading in wires. The 

217 



218 Operating and Testing 

substance of which the leading in wires is composed 
must expand and contract at the same rate as the 
glass surrounding it, otherwise the glass would be 
broken or a space would be left where the air could 
enter the lamp. This substance must also be of such 
a nature as to withstand the high temperature at 
which the glass is fused and the heat of the filament. 
Platinum is about the only material that fulfills these 
conditions and is used for this purpose. 

The filament is now subjected to what is knoAvn as 
the ^^ flashing" process, being placed in a chamber 
filled with a hydrocarbon vapor and current passed 
through the filament until it is heated to a low de- 
gree of incandescence. Any' irl-egular portions of 
the filament will be heated to a higher temperature 
and carbon will be deposited to a greater extent at 
these points. When all parts are uniform and the 
filament is of the proper resistance, the process is 
stopped. In good lamps heated to a dull red, the fila- 
ment should appear uniform throughout. If there 
are bright spots the filament will quickly burn out at 
one of these places. 

After flashing the filament appears gray in color, 
with a hard outer surface w^liich increases the useful 
life of the lamp and adds to its efficiency. 

The filament is now placed in the glass globe and 
the air is then exhausetd by mechanical or chemical 
means. A good vacuum is of great importance. The 
presence of oxygen hastens the deterioration of the 
filament. The presence of any gas inside the lamp 
increases the loss of heat in the filament and there- 
fore reduces its efficiency. This also increases the de- 



Incandescent Lamps 219 

terioration of the filament through friction between 
the filament and the gas. In a poor vacuum vibration 
of the filament will cease quickly. 

Incandescent lamps are rated according to their 
candlepower, the sixteen-candlepoAver lamp being the 
size most generally used. The lamp is also made in 
various sizes from 2 to 50-candlepower. 

The light given out by an incandescent lamp bears 
a certain definite relation to the temperature of the 
filament, being greater as the temperature of the fila- 
ment is increased. The current taken by the lamp 
depends upon the resistance offered by the hot carbon 
filament. It can readily be seen that we might have 
two incandescent lamps, each giving out a light equiv- 
alent to 16-candlepower, but one taking considerable 
more current than the other, as, for instance where 
one lamp has a short filament of small cross section 
and the other a long filament of larger section. It is 
evident that to intelligently compare lamps, the rela- 
tion between the amount of energy consumed and the 
amount of light given out by the lamp must be 
kaown. This is termed the '^efficiency" of the lamp, 
and is obtained by dividing the total watts consumed 
by the lamp by the candlepower. 

Total Watts 



Candlepower 

If a lamp consumes 56 watts and gives a candle- 
power of 16, the efficiency is 56 ^ 16 = 3.5 watts per 
candle. 

It may be noted that the term '^ efficiency" is some- 
what of a misnomer a^ here used. A 16-candlepower 



220 Operating and Testing 

lamp consuming 50 watts, has an efficiency of 3.1, the 
efficiency in this case as expressed numerically being 
less than in the case previously stated, while, as a 
matter of fact, the real efficiency of the lamp is higher 
as it consumes fewer watts per candle. Nevertheless, 
the term has come into general use and when ex- 
pressed in a certain number of watts per candle con- 
veys the actual comparative rating of the lamp. Low 
candlepower lamps are generally less efficient than 
the standard sizes and the 220-volt lamps are less ef- 
ficient than those of 110. Table I shows the wattage 
and current for lamps in general use. 

The efficiency in lamps of the same type of filament 
depends upon the temperature of the filament. The 
higher the temperature the brighter the filament and 
the less the number of watts per candle. A tempera- 
ture of about 2500° F., is maintained in the carbon 
filament. After a lamp has been in use for some time 
the filament gradually disintegrates, the carbon which 
is thrown off by the filament depositing on the inside 
of the glass globe. The light emitted from the lamp is 
thereby greatly reduced and the watts per candle in- 
creased. The disintegration of the filament is more 
rapid the higher the temperature. 



Incandescent Lamps 



221 



TABLE I. 

RATING OF INCANDESCENT LAMPS. 



C. !• 



Carbon Lamps, 110 Volts. 



c. p. 


1 Watts 


Amperes 


2 


13 


.11 


4 


18 


.16 


6 


24 


09 


8 


30 


.27 


10 


35 


.32 


12 


40 


.36 


16 


56 


.51 


20 


70 


.64 


24 


84 


.76 


32 


112 


1.00 


50 


175 


1.60 



Carbon Lamps, 220 Volts. 
Watts 



Gem Lamps, 110 Volts. 



Amperes 



8 


36 1 


.16 


10 


45 


.20 


16 


64 


.29 


20 


76 1 


.35 


24 


00 [ 


.41 


32 


\^2 1 


.55 


50 


100 1 


.86 



C. 1\ 


Watts 


1 Amperes 


20 


50 


1 .45 


40 


100 


.91 


50 


125 


1.14 


75 


187 


1.70 


100 


250 


2.27 





Tantalum Lamps, 


110 Volts. 




C. P. 


Watts 


1 


Amperes 


20 
40 


40 

80 


1 


. 36 
.73 




Tungsten Lamps, 


110 Volts. 




C. P. 


Watts 


■ 1 


Amperes 


32 

48 


40 
60 


1 


.36 
.55 



It is evident from the foregoing that there are two 
main factors effecting the usefulness of an incandes- 
cent lamp. By increasing the efficiency we shorten 
the life and by decreasing the efficiency we increase 
the life of the lamp A lamp taking 3.5 watts per 
candle has a useful life of about 800 hours. By burn- 
ing the lamp at 4 watts per candle the life of the lamp 
would be extended to about 1,800 hours. 



222 



Operating and Testing 



The cost of current will generally determine the 
proper lamp to use. When the cost of current is low, 
a low efficiency lamp may be used, and when the cost 
of current is high, a high efficiency lamp should be 
used. A point to be considered in the use uf high 
efficiency lamps is the pressure or voltage at which the 
lamp is burned. For economical and satisfactory op- 
eration, the pressure must be maintained practically 



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Figure 143 

uniform. With the filament already at a high tem- 
perature even a slight increase in voltage will produce 
a considerable increase in the temperature of the fila- 
ment and a corresponding decrease in the life. This 
is not of so much importance where low efficiency 
lamps are used as a slight increase in the voltage does 
not produce such an excessive rise in the temperature 
of the filament. 



Incandescent Lamps 



223 



The manner in which the candlepower, watts per 
candle, and the life of 3.5 watt carbon lamps vary- 
where burned at voltages greater or less than their 
normal voltage is showTi in Table II, which table is 
given by the AVestinghouse Co. and represents the 
average of a number of tests. The values given in 
the table are plotted on the curves in Figure 143. It 
will be noted that an increase of 3 per cent in the 
voltage reduces the life of the lamp to one-half, while 
an increase of 6 per cent decreases the life to one-third. 

TABLE II. 

INCANDESCENT CAKBON LAMPS. 

Effect of Variation of Voltage on Candle Power, Efficiency and Life. 





Candle 


Watts per 




Volts 


Power 


Candle 


Life 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


110 


169 


72 


15 


109 


161 


74 


18 


108 


153 


76.5 


21 


107 


145 


79 


24.5 


106 


138 


81.5 


29 


105 


131 


84 


34 


104 


124 


87 


40 


103 


118 


90 


48 


102 


111 


93 


60 


101 


106 


96.5 


80 


100 


100 


100 


100 


99 


95 


103 


120 


98 


90 


106 


147 


97 


85 


109.5 


175 


96 


80 


113.5 


200 


95 


7o 


118.5 


270 


94 


71 


123.5 


355 


93 


67 


128 


450 


92 


63 


134 


545 


91 


59 


140.5 


650 


90 


55 


1 147.5 


760 



As an illustration of the use of the table assume 
the case of a 16-C. P., 110-volt lamp consuming 3.5 
watts per candle and having a life of 800 hours. If a 
lamp of this rating was burned on a circuit where the 



224 Operating and Testing 

voltage was 120, or 109 per cent of its normal voltage, 
the candlepower would be increased to 161 per cent 
of the normal or 25.8 C. P. ; the watts per candle 
would be reduced to 74 per cent, or about 2.59 ; the 
life would be decreased to 18 per cent, or 144 hours. 

If a 16-C. P., 3.5 watt lamp, designed for use on an 
115-volt circuit, was burned on a circuit at 110 volts 
or 95.5 per cent of the normal, the candlepower would 
be decreased to 77.5 per cent or 12.4; the watts per 
candle to 116 per cent, or about 4; the life increased 
to 237 per cent, or about 1,880 hours. 

It is an inexcusable, though very natural, mistake 
to suppose that there is any economy in burning lamps 
after their candlepower has been greatly reduced. As 
a rule, if a lamp be burned about 1,000 or 1,200 hours 
the candlepower will have fallen to one-half of its 
initial value, while the current consumption will re- 
main about the same. Consider the following exam- 
ple : A 50-watt lamp burning 600 hours will consume 
30,000 watts, which at ten cents per kilowatt will cost 
$3.00. The cost of the lamp will not be more than 20 
cents. If now the lamp be burned for 600 hours 
more, it will give out about 8 candlepower and the 
cost of the current consumed will be another $3.00, 
whereas the cost of a new lamp of 8 candlepower, 
which would give its equivalent in light, would cut 
the cost of current do^^TL to one-half or $1.50 and the 
cost of the new lamp would be only 20 cents. It will 
be seen that the user, who is trying to save something 
by getting along with a dim light, is losing half his 
light to save 20 cents, and at the same time paying out 
$1.30 more than would be required to obtain the same 



Incandescent Lamps 225 

illumination with a new lamp of the same candlepower 
as the old one is actually giving him. 

The useful life of a lamp is determined by the num- 
ber of hours the lamp will burn before the candle- 
power has dropped to 80 per cent of its original value. 
This is knoAATi as the ^^ smashing point/' and it is sel- 
dom economical to burn the lamp after this point has 
been reached. 

When lamps become old and dim, the candlepower 
can be increased by increasing the voltage, but this is 
poor practice for, of necessity, the voltage on w^hat- 
ever new lamps may be in circuit is also increased and 
this does more harm in shortening the life of these 
lamps than good in saving the old. 

The efficiency and the life of incandescent lamps 
are two factors which do not harmonize. The higher 
the efficiency of a carbon filament lamp the shorter 
its life. This makes it advisable to carefully consider 
which is the most economical lamp to use. The two 
main considerations in determining the most econom- 
ical lamp are the cost of current and the cost of lamp 
renewals. Tables III and IV are prepared to facili- 
tate calculation in this regard. The most economical 
lamp to use is that in which the cost of energy and 
the cost of renewals is a minimum. If the cost of 
power is high, a lamp of high efficiency, even though 
its life be short, is generally more economical; while 
if power is very cheap, a lamp of low efficiency is gen- 
erally advisable. 

TABLES 

In Table III, the cost of current per kilowatt is 
given at the top of the columns, and the watts per 



226 Operating and Testing 

candlepower of the lamp in the left-hand vertical col- 
umn. Wherever two columns cross will be found the 
cost per candlepower for 1,000 hours for the lamp of 
an efficiency as indicated in the left-hand column, and 
at the cost per kilowatt as shown at the top of the 
column. As an example : Take a lamp of an effi- 
ciency of 3.1 watts per candle, with current costing 
10 cents per kilowatt. "Where these two columns in- 
tersect in the table will be found the value, .310 ; show- 
ing that the cost per candlepower per 1,000 hours at 
this efficiency and rate will be 31 cents. 

To ascertain the cost of current consumed by a 
lamp of any candlepower per 1,000 hours, the cost as 
found in the table must be multiplied by the candle- 
power of the lamp. For instance : a 16-candlepower 
lamp at the rating shown above, would cost 16 X .31 
= $4.96 for 1,000 hours burning. 

Table IV deals with the cost of lamp renewals. In 
the upper horizontal row is given the life of the lamp 
in hours, and at the left hand vertical column the 
cost of the lamp in cents per candlepower. AVherever 
the two columns cross Avill be found the cost of lamp 
renewals per 1,000 hours. 

Example: Suppose a 16-candlepower lamp costs 19 
cents (1.2 cents per candle) and has a life of 600 
hours. In the row at the right of 1.2, and in the col- 
umn headed 600 will be found the value, .02, which 
is the cost of the lamp renewals per candlepower for 
1,000 hours. For a 16-candlepower lamp, the cost 
would be 16 X .02 == $0.32. The total cost of the 
lamp for 1,000 hours, including both cost of current 
and renewals, is $4.96 + $0.32 = $5.28. 



Incandesce lie Lamps 



99' 





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228 



Operating and Testing 






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To find the most economical lamp where the cost of 
current is fixed, it is only necessary to try out several 
cases and select the one where the sum of the two fac- 



Incandescent Lamps 229 

tors is a minimum. In comparing lamps of either the 
same or different candlepowers, it is not necessary to 
multiply the values found in the tables by the candle- 
power of the lamp. On the other hand, where the 
actual cost per 1,000 hours is desired, the values 
found in the tables must be multiplied by the candle- 
power of the lamp in question. 

As an example showing the method in which the 
table is used the two following lamps will be com- 
pared : 

Sixteen-candlepower carbon lamp of an efficiency 
of 3.5 watts per candle, life of the lamp 1,150 hours, 
cost of the lamp 16 cents (1 cent per candle). 

Thirty-two-candlepower Tungsten lamp of an effi- 
ciency of 1.25 watts per candle, life of lamp 1,000 
hours, cost $1.20 (3.7 cents per candle). 

Cost of current, 10 cents per kilowatt. 

For the carbon lamp : 

Table III gives 35 

Table IV gives 009 

Total 359 

For the Tungsten lamp : 

Table III gives 125 

Table IV gives 035 

Total 160 

The result shows that for the values taken the cost 
of the Tungsten lamp will be less than one-half that 
of the carbon lamp. 



230 Operating and Testing 

It will be noted that in nsing the tables, the cost 
per candlepower of the Tungsten lamp is 3.7 cents is 
not given in the table, and the value 3.5 is taken. If 
greater accuracy is desired, the values may be inter- 
polated. For instance : in the case given, the value 
from Table IV would be .037, giving a total of .162 
in place of .160. 

Arc lamps, Nemst lamps, or, in fact, any lamps 
where the candlepower, efficiency and cost are known 
may be compared ; either two lamps of the same type, 
or lamps of different types. 

METALLIZED FILxVMENT LAMP 

In the past few years a number of new types of 
incandescent lamps have been developed. The qual- 
ity of the light, the life of the lamp, its regulation 
and its efficiency have all been greatly improved. The 
first of these lamps to come into general use is known 
as the metallized filament lamp. The filament of this 
lamp is of carbon, which is put through various proc- 
esses, one of which is the heating of the filament to a 
very high degree in an electric furnace. Practically 
all the impurities are driven out by this process and 
a greatly increased efficiency is obtained, and the fila- 
ment gives out a much better quality of light. 

One of the peculiar results effected by the treat- 
ment of the filament, and the one from which it gets 
its name, is that the electrical characteristics of the car- 
bon is considerably changed. The ordinary carbon 
filament has a negative temperature coefficient; in 
other words, its resistance lowers with an increase in 



Incandescent Lamps 231 

temperature and increases with a lowering tempera- 
ture. On a system where the voltage regulation is 
poor, the effect of the negative temperature coefficient 
is, so far as the light is concerned, cumulative, the in- 
crease in voltage causing, in itself, more current to 
flow through the lamp, increasing its candlepower. 
The increase in current increases the temperature of 
the filament and lowers its resistance, this causing a 
still further increase in the candlepower. 

The metallized filament has a positive temperature 
coefficient, similar to metals. Its resistance increases 
as its temperature increases. The regulation of the 
lamp is therefore much better than that of the carbon 
lamp, an increase in voltage causing an increase in 
the resistance of the filament and a corresponding ten- 
dency to check the current rise. This lamp has 
an efficiency of 2.5 watts per candle, or 40 watts for 
a 16-candlepower lamp. 

TANTALUM LAMP* 

The Tantalum lamp is another recent development 
in the field of incandescent lighting. This lamp takes 
its name from the metal from which the filament is 
constructed. Tantalum is one of the rare metals and 
not only has a greater strength than steel, but is. capa- 
ble of withstanding a very high temperature. Due to 
these characteristics the metal is very well suited for 
use as a filament. 

As all metals are of comparatively low resistance 
a filament of unusual length must be employed to ob- 
tain the proper resistance. The Tantalum lamp has 



232 Operating and Testing 

an efficiency of 2 watts per candle and gives a very 
white light resembling daylight. It is not recom- 
mended for use on alternating current circuits. 

TUNGSTEN LAMPS 

Shortly after the introduction of the tantalum lamp 
a still greater advance was made by the bringing out 
of the Tungsten lamp. Tungsten, another of the rare 
metals, is in its electrical behavior similar to tantalum 
but for use as a filament it surpasses tantalum, owing 
to the fact that its melting point is considerably 
higher. The filament can be burned at a very high 
temperature and has an efficiency of 1.25 watts per 
candle. The filament being of metal has a compara- 
tively low resistance and, as with tantalum, must be 
unusually long to obtain the proper resistance for use 
on the common voltages. 

The current required for producing equal candle- 
power with Tungsten lamps is approximately one- 
third of that required by carbon lamps, and approxi- 
mately one-half of that required by the metallized 
filament lamps. The cost of operating Tungsten lamps 
is, therefore, much less than the cost of operating 
other lamps. 

The light given by the Tungsten lamp is much 
whiter and more pleasing in character than that given 
by other lamps. As its quality corresponds more 
nearly to sunlight than any other artificial illuminant 
it is especially desirable for use in show rooms, stores, 
etc. The loss in candlepower after the lamp is in use 
for some time amounts to about one-fourth that of the 



Incandescent Lamps 233 

carbon lamp. The lamp also has a much longer life 
than the carbon lamp. In regulation the Tungsten 
lamp is greatly superior to the carbon lamp and an 
excessive voltage which would ruin a carbon lamp 
does not seriously affect the Tungsten lamp. 

Tungsten being quite brittle and the filament of 
necessity being of small cross section, the lamp must 
be carefully handled. The lamp should be cleaned 
while hot, as the filament is then stronger than when 
cold. It is also advisable to control the lamp from 
switches, thus avoiding the jarring caused by turning 
on at the socket. It has been customary to burn the 
lamp with the filament hanging do\^TLward in a verti- 
cal direction this being necessitated by the sagging of 
the filament, but lamps are now made to burn with 
the lamp hanging in any direction. The filament 
after having burned for some time shrinks considera- 
bly and this must be provided for in the manufacture. 

AYith Tungsten lamps designed for use on low volt- 
age, the filaments are made of a much shorter length 
and are less liable to breakage. This class of lamp 
may be burned in series on the ordinary circuits of 
110 or 220 volts, or suitable transformers are now 
made so that on alternating current systems these low 
voltage lamps may be wired up in multiple. 

The filaments of both tantalum and tungsten can 
often be welded when broken, by shaking the lamp 
when connected in circuit, until the broken ends come 
together. As this operation generally has the effect 
of shortening the filament and lessening its resistance 
it brings with it an increase in candlepower. 



233a Operating and Testing 

NITROGEN-FILLED LAMPS 

The lately developed nitrogen-filled lamps have 
caused considerable comment by their extreme bril- 
liancy and high efficiency. The larger sizes of these 
lamps operate at a considerable advantage over all 
other incandescent illuminants. 

The intrinsic brilliancy is very high and they should 
preferably be hung high enough to be out of the range 
of vision ; otherwise they will be injurious to the eye. 

The temperature of the enclosing globes is very high, 
and if used out of doors where they may be struck by 
sleet or rain while hot they are likely to be broken. 

It is best to use these lamps only in special sockets 
containing no material w^hich may be affected by the 
heat, and where wires are run close enough to be 
affected by the heat the ordinary rubber-covered wire 
should not be used. Asbestos-covered wire is prefer- 
able. 

The color value of these lamps is very good and they 
are well suited for color-matching and also for photo- 
graphic work, although for the latter purpose they 
are not as fast as some types of arc lamps and the 
mercury vapor lamps. 

The distribution of light from these lamps is quite 
uniform in nearly all directions and is emitted from 
a point source more nearly than that of any other 
lamp except the arc lamp. It will, therefore, throw 
strong shadows, and requires special reflectors. 

The efficiency of the smaller lamps is not much 
better than that of the ordinary mazda, or tungsten, 
lamps, but the light is more concentrated and a 



Incandescent Lamps 233b 

greater brilliancy is obtainable. This fact makes them 
very desirable for show-window lighting. 

The following table gives approximate data concern- 
ing nitrogen-filled tungsten lamps: 



/olts 


Size of lamps 
in watts 


Efficiency in 
watts, per c. 


Amperes per 
lamp approx. 


105 
to 
125 


400 

500 

750 

1000 


.75 
.70 
.60 
.55 


31/2 

41/2 



234 



Operating and 'Testing 



ILLUMINATION 

Light, so far as its practical use is concerned, de- 
pends upon its value as a means of discrimination 
both as to form and color. The amount of light which 
is useful for this purpose is known as the illumina- 
tion, and depends upon the quality and strength of 
the light giving source, and its distance from the ob- 
ject to be illuminated. 

The unit of illumination is the candle foot, being 
the amount of light received by a surface placed at a 
distance of one foot from a light of one standard can- 
dlepower. The illumination on any surface is in- 




Figure 144 

versely proportional to the square of its distance from 
the source of light. This is plainly shown in Figure 
144. If the surface A is so located that all points on 
it are at a distance of one foot from the one candle- 
power light L, the intensity of the light on this sur- 
face will be one candle foot. The surface B, located 
at a distance of two feet from the light L is illumi- 
nated over a surface four times that of surface A and 
the illumination is, therefore, decreased to one-fourth ; 
or in the inverse ratio of the square of the distances 
from the source of light. 

A 16-candlepower lamp would produce an illumi- 



iThcandescent Lamps 



235 



nation of one candle foot on a surface located four 
feet away from the lamp, and this is considered suf- 
ficient for all ordinary purposes, but for brilliant il- 
lumination much greater intensities are often used. 
Table V gives, for different classes of lighting, the 
amount of illumination in candle feet and the corre- 
sponding area in square feet for each 16-candlepower 
lamp, to produce this illumination. 

TABLE V. 

Square feet per 
lamp, lamps four 
feet above object. 

Halls 1 to 3 candle feet 60 to 20 

Reading 1 to 3 candle feet 60 to 20 

Desk - ... 2 to 4 candle feet 30 to 15 

Book keeping 2 to 4 candle feet 30 to 15 

Clothing stores 4 to 6 candle feet 15 to 10 

Drafting, engraving 5 to 10 candle feet 12 to 6 

In using this table the color of the walls must be 
taken into consideration. With dark walls, the great- 
est number of candle feet should be used. 



30* 15* d 




60* 



60'' 



45' JO' 15' 0' /5° JO' 45^ 
Figure 145 

With an incandescent lamp the light is not given 
out uniformly in all directions. The distribution of 



236 



Operating and Testing 



light from a 20-candlepower metallized filament 
lamp is shown in Figure 145, where the candle- 
power taken at various angles in a vertical plane 
are plotted. The concentric circles represent the can- 
dlepower marked on them 

The curve of light distribution varies in the several 
types of lamps, and is greatly affected by the shape of 
the filament. It will be seen from the curve, Figure 
145, that a considerable amount of light is given out 



75' 


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30' 



in a horizontal direction while, as a general rule, the 
greatest light is desired below the lamp. By the use 
of suitable reflectors almost any distribution of the 
light desired may be obtained and the effect, so far 
as the candlepower at points below the lamp is con- 
cerned, is clearly shown by the curve. Figure 146. 
Here the maximum light is given off at an angle of 
40"^ and the lamp is much more useful for ordinary 
purposes. 



Incandescent Lamps 



237 



The amount of illumination at any given point over 
an area will depend upon the candlepower of the 
lamp, the distance from the lamp and the angle that 
the surface makes with the line of the direction of the 
light. The first two factors have been explained and 
the last one will be readily understood from every day 
experience, it being Avell known that the greatest 
amount of illumination, in reading, for instance, is 
obtained when the paper or book is so held that the 
light strikes it at right angles. The curve. Figure 147, 
represents the illumination at various points at differ- 
ent distances from the source of light. If two similar 
lamps are placed 16 feet apart, the resultant illumina- 



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Figure 147 
tion will be equal to the sum of the two curves A and 
B or as shown by curve C. 

To lay out a curve of this kind it is necessary to 
know first the curve of the distribution of the particu- 
lar lamp used. It is also necessary to know the pro- 
portion of light reflected at right angles to the surface, 
where the light strikes the surface at an angle. 

That the color of the walls and ceiling of a room 
has a great effect on the amount of useful light is 
shown from Table VI, which gives the coefficient of 
reflection for various colors. As the light reflected 
from the w^alls and ceilings is but a small proportion 



238 Operating and Testing 

of the total light, the values shown are only useful in 
comparing the several wall colors. The size of the 
room and the use of reflectors will also greatly modify 
the effect of the wall coloring. 

TABLE VI 

Coefficient of 
Color of Wall. Eeflection 

"White paper 70 

Chrome yellow 62 

Orange paper 50 

Plain deal (clean) 45 

Yellow paper 40 

Yellow painted wall (clean) 40 

Light pink paper 36 

Plain deal (dirty) 20 

Yellow painted wall (dirty) 20 

Emerald Green Paper 18 

Dark brown paper 13 

Vermilion paper , 12 

Blue green paper 12 

Cobalt blue paper 12 

Deep chocolate paper. .04 

Good illumination requires that the light be of suf- 
ficient strength to plainly discern the object illumi- 
nated. The light must be uniform. A flickering or 
streaky light is very bad on the qjq^. The light should 
not be exceedingly strong, as a strong light is very 
injurious to the eye ; nor should the light be too dim, 
as the eye strain is considerably increased. The lights 
should always be so arranged that the direct rays of 
light do not fall on the eye. 



CHAPTER XVII 

NERNST LAMP 

Figure 148 shows a diagram of the Nemst Lamp. 
The glower G (which emits the light) is composed of 
an oxide which when cold is of quite high resistance, 
but this resistance is lowered as the temperature rises. 

When the switch is closed the current passes 




through the fine wire of the heater H which soon heats 
the glower so that current begins to flow through it. 
When this current attains approximately its normal 
value the magnet M attracts the cut-out C and in so 
doing opens the heater circuit and prevents further 
consumption of energy. B is a fine iron wire resist- 
ance which serves to steady the current. The resist- 

239 



240 Operating and Testing 

ance of the iron wire increases as the current increases 
and thus exerts a steadying effect. 

This lamp gives out a very serviceable white light 
and is of much higher efficiency than the ordinary 
carbon filament incandescent lamp. A glower that 
consumes about 88 watts is supposed to yield about 
60 candlepower. 

The starting current is always about 20 per cent 
in excess of the normal operating current. 

These lamps can be had in a great variety, of sizes, 
either for 110 or 220 volts, and for either direct or 
alternating current. On alternating currents the life 
of the lamp is, however, much longer than on direct 
current circuits. 

As the glowers are always located at the bottom of 
the frame the distribution of the light is very good 
and reflectors are not needed. 

COOPER-HEWITT LAMP 

Figure 149 shows a diagram of the connections of 
the Cooper-Hewitt Lamp for direct currents. These 
lamps each contain a small quantity of mercury 
through which the current must be established for a 
short time and then broken. This is accomplished by 
tilting the tube slowly so that the mercury in it run- 
ning from the high to the low side forms a continuous 
stream and allows the current to start. After the cur- 
rent is started the mercury continues to run to the 
low end and finally breaks the circuit ; but the current 
now continues to flow and produces a greenish light 
of very high actinic quality. The lamp is extremely 
w^ell suited for photographic purposes. Great care 



Cooper-Hewitt Lamp 



241 



■must be exercised that the lamp is connected properly 
with reference to polarities. Current passing through 
it in the wrong direction will quickly ruin the lamp. 
The circuit can readily be traced in the figure. When 
the main switch is closed and before the lamps are 
tilted the current passes through the resistances R and 
the contacts il. When one of the lamps is tilted and 
current established through it the magnet is energized 
and attracts the armature M, thus cutting out the 




Figure 149 

path through the small resistance in parallel wdth the 
lamp. Should one lamp fail to work, the current 
through the magnet would cease and the armature fall 
thus closing the circuit so that the other lamps may 
remain in use. The main switch should never be left 
closed while the lamps are not in use as current would 
be continuously flowing. 

The lamps must not be used with the negative elec- 
trode tilted too high up. 



242 Operating and Testing 

The current should never be allowed to exceed 4 am- 
peres and should normally not exceed 3%. The re- 
sistances E are adjustable and should be set for this" 
current value. 

These lamps are sometimes arranged to be started by 
a high induced E.M.F., an induction coil is arranged 
to send a momentary kick of current through the tube 
which starts the lamp. Sometimes, also, two lamps are 
mounted on one frame and started together. In suck 
a case the shunt circuit around the lamps may be 
omitted. The life of the tubes is said to be about 
1600 hours. 



CHAPTER XVIII 

INSTRUMENTS FOR TESTING 

Probably the easiest and simplest way of testing is 
by ' ' tasting. ' ' This is done by placing the two ends 
of the wire being tested on the tongue. The- passage 
of current from one wire to the other over the tongue 
decomposes the saliva on the tongue and leaves a salty 
taste. This salty taste is an indication of current 
flowing. If there are several cells of battery connected 
to the line one wire may be held in the hand and the 
other placed on the tongue or, if one terminal of the 
batteries is grounded, a person standing on wet or 
moist ground can taste the current by placing one wire 
on the tongue. 

Obviously this test is very limited, being used as a 
rule only in bell work to ascertain if current is ob- 
tainable at a certain point. Some care must be exer- 
cised, in using a test of this kind, not to allow the 
wires to come together on the tongue, as a considerable 
spark is obtained w^hen a circuit containing magnets 
is broken. 

Another test in which the chemical effect of the cur- 
rent may be used to determine both the presence of, 
and the direction of, flow of current consists in holding 
the two ends of wire being tested in a cup of water or 

243 



244 Operating and Testing 

a solution of water and salt or water and acid. The 
presence of the current will be indicated by the for- 
mation of hydrogen bubbles on one of the terminals 
and owning to the fact that the bubbles form on the neg- 
ative terminal the direction of flow^ of the current can 
be ascertained. 

The chemical effect of the current is also made use 
of to determine the amount of current flowing. The 
Edison chemical meter, which is now almost out of 
use, consists of two plates of zinc suspended in a solu- 
tion of water and acid and so connected to the main 
circuit as to allow a certain definite proportion of the 
main current to flow between the plates. The amount 
of zinc deposited on the negative plate measures the 
amount of current that has passed through the meter. 

The heating effect of the electric current is some- 
times made use of in testing, the mere fact of a con- 
ductor being hotter than the surrounding atmosphere 
generally indicating the presence of current and 
roughly the amount. 

By making use of the magnetic properties of the 
current several more convenient and satisfactory 
methods of testing are available. Probably the sim- 
plest of any of these methods consists of the ordinary 
vibrating electric bell, such as is used for call bells, etc., 
or a telegraph instrument. The use of a telegraph in- 
strument has some advantages over the bell in that it 
is more sensitive to small currents and, by varying the 
adjustment of the spring on the sounder the compara- 
tive strength of the current may be roughly deter- 
mined. 

One of the oldest testing instruments is the com- 



Instruments for Testing 245 

pass. This in its simplest form consists of a piece of 
magnetized steel pivoted or suspended so that it can 
turn about its central point. The compass needle being 
magnetized sets up a field of force in which the lines 
of force emanate from the north pole, and encircling 
the needle enter at the south pole. As the earth itself 
is surrounded by lines of force extending from the 
north pole to the south pole, the compass needle being 
free to move tends to set itself in a north and south 
position. A wire carrying current is surrounded by a 
field of force as has been explained in previous chap- 
ters. When a compass is brought into the field of 
force the needle assumes a position due to the result- 




Figure 150 

ant field. By means of Ampere's rule, which is given 
below, the direction of the current flow can be easily 
determined. 

Ampere's rule : If a person swims with the current 
and looks at a north seeking pole it will be deflected to 
the left. The relation existing between a wire carry- 
ing current in a certain direction and a compass nee- 
dle held either above or below it is shown in Figure 
150. The direction in w^hich the needle tends to point 
is reversed by changing it from above to below the wire 
or vice versa. 

The expansion of a wire due to the heating effect of 
the current flowing in it is made use of to indicate the 



246 



Operating and Testing 



amoimt of current flow in the so-called ^^hot wire" 
instruments. 

A wire of some length is rigidly fastened at one 
end, the other end being attached to a spring. A 
pointer is attached to the wire at the point where it 
and the spring connect On sending a current through 
the wire it becomes slightly heated and expands, the 
amount of expansion being indicated by the position 
of the pointer on a suitably graduated scale. Neces- 




Figure 151 

sarily the resistance of the instrument is quite low. 
Instruments of this kind are ''dead beaf and are un- 
affected by external fields. They can be used on 
either direct or alternating current. 

Practically all measuring instruments in use at the 
present time operate on the principle previously de- 
scribed in connection with the compass needle. 

In Figure 151 is shown a tangent galvanometer. The 
wire is wound on the outside of the large ring and 
may consist of a number of turns of small wire or a 
few turns of large wire, or, as is sometimes the case, 



Instruments for Testing 247 

two separate windings may be used, one of fine wire 
and one of large wire. In the center of the ring is 
placed a compass needle. The length of this needle is 
small as compared with the diameter of the ring so 
that whatever position it may assume, the needle is 
always in a practically uniform field. A light pointer 
attached to the needle moves over a graduated scale. 

"When the galvanometer is used it is placed in such 
a position that the coil lies parallel with the lines of 
force of the earth's field, i. e., points north and south. 
The current flowing in the coil is proportional to the 
tangent of the angle of deflection of the needle and it 




Figure 152 

is from this fact that the instrument derives its name. 

The meaning of the tangent is explained by Figure 
152. The tangent of an angle is the length of the line 
from F to where a line drawn from the center of the 
circle through the angle in question intersects the line 
F G. Thus a current deflecting the needle to the point 
2 on the circle is proportional to the length of the line 
F 1 and not to the space between F 2. This type of 
galvanometer is used only in the laboratory or testing 
room. 

"Where it is desired to measure very small currents, 
as where very high resistances are to be measured, a 



248 



Operating and Testing 



galvanometer more sensitive than the tangent galva- 
nometer must be used. The mirror galvanometer is 
often used for this purpose. 

Figure 153 shows the principle of the D'Arsonval 
galvanometer. The field of this instrument consists 
of two permanent magnets between the poles of which 
is suspended a coil of fine wire. This coil is suspended 




Figure 153 

by a wire from the screw sho\^Ti at the top of the in- 
strument in the illustration. The current being meas- 
ured passes down through this suspension wire, 
through the wire of the coil and out by means of a 
spiral spring which is connected to the lower end of 
the coil. A very light mirror attached to the movable 
coil serves as a means to determine the extent of the 
deflection. Either of two methods may be employed. A 



Instruments for Testing 249 

lamp and a graduated scale are so arranged that a 
beam of light coming through a slit in a hood over the 
lamp falls on the mirror and is reflected on the scale. 
A telescope may be used in place of the lamp. The 
telescope is focused so that the scale is visible in the 
mirror. The slightest movement of the mirror can 
then be accurately read through the telescope. 

Practically all of the instruments just described are 
made use of only in the laboratory and are not suitable 
for ordinary switchboard and testing purposes. To 
be of commercial use an instrument must not be seri- 
ously affected by the earth's magnetism nor b}^ the 
presence of large masses of metal or strong magnetic 
fields such as are apt to be found in a dynamo room 
for instance. The instrument must be portable, and 
the accuracy of the indications must not change un- 
duly with continued use. The instrument must also be 
easily read and unnecessary calculations avoided. 

Commercial instruments are divided into three gen- 
eral classes, those for use on direct current, those for 
use on alternating current only, and those for use on 
either direct or alternating current. In each of these 
three classes instruments are designed for special pur- 
poses, such as the mesurement of voltages, measure- 
ment of current strength and measurement of elec- 
trical power. Although the principles upon which 
these various instruments operate are the same, still 
there are some differences in their construction de- 
pending on the purposes to which the instruments are 
to be put, as will be described further on. 

Almost any of the galvanometers previously de- 
scribed could be used for the measurement of direct 



250 



Operating and Testing 



current voltages, but, for the reasons already assigned, 
most of them are impracticable for general use. 

In Figure 154 is shown the well known Weston in- 
strument. A permanent magnet M, constructed of a 
specially prepared steel having the property of retain- 
ing its magnetism for an indefinite time, is fitted W7th 
soft iron pole pieces. In the space between the pole 
pieces, held in place by a non-magnetic metal such as 
brass, is a soft iron core. A coil of fine copper wdre 
w^ound on a copper form is movable in the air gap be- 
tween the inner core and the pole pieces. In order 




Figure 154 

that the resistance to turning due to friction be re- 
duced to a minimum the coil rests in jewel bearings. 
Two fiat spiral springs, one above the coil and one be- 
low it, serve the double purpose of providing a torque 
against which the coil must act and also carry the 
current to the movable coil. A light pointer fastened 
to the shaft upon which the coil revolves moves over a 
scale graduated in divisions suitable to the purpose to 
which the instrument is put. 

Copper wire being used in the winding of the coil 
some -resistance must be connected in series with this 



Instruments for Testing 251 

coil where the instrument is to be used, to measure 
comparatively high voltages. This resistance is usually 
inserted in the instrument and consists of a resistance 
wire having a very low temperature coefficient, or, in 
other words, a wire of such composition that its re- 
sistance will be but little affected by changes in its 
temperature. The importance of using a wire of this 
kind can readily be seen, for, should an instrument 
which had been calibrated at a temperature of 70° be 
used in a room at a temperature of about 100°, the de- 
crease in current flowing through the instrument due 
to the increase in resistance in the heated w^ire would 
seriously affect the accuracy of the instrument. 

The amount of resistance connected in series with 
the coil varies and depends on the voltages which it 
is intended the instrument should measure. In volt- 
meters for use on 500 and 600 volt circuits, this resist- 
ance is equal to about 65,000 or 75,000 ohms, thus 
allowing a current of about .007 ampere to pass 
through the instrument. 

Current enters the instrument through the binding 
posts and passes through the resistance R, spiral 
springs and the coil. The magnetic field produced by 
the current flowing around the coil acts in conjunction 
with the field of the permanent magnet and tends to 
revolve the coil in a manner similar to that of the 
armature of a motor. As a matter of fact, this meter 
is simply a motor having a permanent field, and an 
armature that can make only a partial revolution. The 
amount of deflection will be proportional to, the cur- 
rent flowing through the wire of the coil, and as the 
coil always moves in a practically uniform field a uni- 



252 Operating and Testing 

form scale will result. The movement of the coil is 
restrained by the spiral springs 

This instrument is what is termed ^^dead beat/' 
that is, the tendency of the pointer to swing backward 
and forward on defleC'tion is reduced to a minimum. 
The movable coil is wound on a copper frame. When 
on deflection of the instrument this frame moves across 
the field of the permanent magnet, it cuts through 
lines of force and a current is produced in the closed 
circuit of the copper frame, this action tending to re- 
strain the movement of the coil. 

Figure 155 shows a type 'of instrument similar to 
the one just described but varying in some details. M 




Figure 155 

is a permanent magnet fitted with pole pieces of the 
shape shown in the figure, the pole S, S being shaped 
like an iron washer. A coil, C, is attached to a shaft 
which turns in jeweled bearings. A pointer attached 
to the shaft moves over a suitable scale. Current pass- 
ing through the coil C causes it to revolve around the 
pole piece S, S. The instrument is made ^^dead beat" 
by the short circuiting of the copper frame on which 
the coil is wound. 

A type of induction meter which is used only on al- 
ternating current circuits is shown in Figure 156. A 
copper or aluminum disc fastened to a shaft, rotates 
in jewel bearings. Projecting over the disc on one 



Instruments for Testing 



253 



side and so arranged that the disc rotates between its 
pole pieces is a laminated magnet C, on which is wound 
a coil of wire. Another coil C is placed so that its 



i| 



i 



Figure 156 
field cuts the disc. Both coils are connected in par- 
allel. Owing to the fact that with an alternating cur- 
rent flowing through the instrument there wall be a 
difference in phase in the current flowing in coil C and 




Figure 157 

coil C, coil C having no iron core, a torque is set up 
which tends to rotate the disc, the amount of deflec- 
tion being indicated by the pointer attached to the 
shaft. 



254 Operating and Testing 

Figure 157 shows in a simplified form an instrument 
which can be used for the measurement of either direct 
or alteiTiating currents. The current to be measured 
is carried through a solenoid S. In the center of the 
solenoid is suspended a soft iron core, which is free to 
move up or down, the motion of the core being regis- 
tered by the pointer attached to the supporting arm. 
A counterweight serves to balance the iron core. 

When current flows through the solenoid the iron 
core is drawn down into it, the amount of current 
flowing being indicated by the pointer. 

The principle upon which this instrument operates 
is made use of in a number of different instruments. 
As the action of the solenoid is the same when either 
direct or alternating current is used, this instrument 
may be used on circuits of either system. 

Instruments of the design just described have the 
objection that when used on direct current, with an 
increase in current strength, the instrument will indi- 
cate lower than it should, while with a decreasing cur- 
rent it will indicate higher. This is due to ''hysteri- 
sis" in the iron core, and if the core contains any 
great quantity of iron, makes the instrument value- 
less as a voltmeter. "With direct current more accu- 
rate results may be obtained by flrst increasing the 
current, then decreasing it and taking an average of 
the readings. On alternating current systems, this 
objection does not exist, but in this case the iron core 
must be laminated to avoid the generation of eddy 
currents. 

The Weston instrument having a permanent mag- 
net field cannot be used for alternating current meas- 



Instruments for Testing 



255 



urement. Figure 158 shows the construction of the 
instrument desiged for use on alternating current cir- 
cuits. An outer coil C is wound on a circular form. 
Inside of this coil, mounted on jewel bearings, is a 
movable coil C. Two spiral springs convey the cur- 
rent to the movable coil and restrain its motion. The 
two coils are connected in series. When current flows 
through the coils, the movable coil tends to take up a 
position parallel with the stationary coil. When used 
on alternating currents, the polarity of each coil re- 
verses at the same time, so that the effect is the same 




Figure 158 

as though direct current was used. The instrument is 
damped by a metal vane moving in a partly closed air 
chamber. 

The difference between a voltmeter and an ammeter 
is merely a difference in winding. A voltmeter is 
wound with a very fine wire and registers the differ- 
ence in pressure between two wires. The finer the wire 
or the greater the number of turns, the more econom- 
ical is the instrument in operation. It needs only to 
produce magnetism enough to deflect the pointer suf- 
ficient to admit of accurate calibration. 



256 



Operating and Testing 



If in any circuit the pressure is greater than the 
range of any accessible meter, several of them may 
be connected in series and the readings of all of them 
added. It is also possible to measure the voltage be- 
tween two wires in the manner shown in Figure 159. 
The voltmeter here measures the difference of potential 
around one lamp and if all lamps are exactly the same 
this need be but multiplied by the number of lamps in 
series to obtain the voltage over the whole group. If 
more accurate results are desired, the voltage around 
each lamp may be taken and all of them added. 
Should, however, the lamp at the voltmeter break 



0-K>-r-0 O 




Figure 159 

while the meter is connected arciund it, the voltmeter 
might be quickly burned out. 

There are two classes of commercial ammeters. One 
of these, not extensively used, is cut in series with the 
line and all of the current passes through it. Such 
ammeters have very few turns of wire and are sel- 
dom used on heavy currents. The kind in most 
extensive use at present is known as the ' ' shunt ' ' am- 
meter. This type of ammeter takes only a small frac- 
tion of the current, the bulk of it passing through the 
'^ shunt." Such a shunt is shown in Figure 160 and 
the manner of attaching the cords leading to the am- 
meter is also shown. The shunt must be designed for 



Instruments for Testing 257 

the particular instrument with which it is to work. 
Nothing must be allowed to disturb the relative resist- 
ance of shunt and instrument and the cord sent with 
them should always be used full length, or the read- 
ings will be inaccurate. 

The measuring capacity of any ammeter may be in- 
creased by providing a suitable shunt. If the resist- 
ance of the shunt is made l/9th that of the ammeter, 
the leadings must bi^ multiplied by 10 to obtain the 
flow of current, if l/99th by 100, or l/999th by 1000. 

If the capacity of one ammeter is insufficient to 
measure the current, several of them may be con- 




Figure 160 

nected in parallel, but each must be provided with its 
own shunt. 

Two ammeters must never be connected to one 
shunt. 

WHEATSTONE BRIDGE 

For the measurement of resistances ordinarily met 
with the Wheatstone bridge is generally used The 
principle of its operation, if thoroughly understood, 
wall greatly assist in comprehending its uses. 

In Figure 161, a battery is connected in series with 
a resistance AB. If the battery has a difference of 
potential of one volt, and AB has a resistance of 10 
ohms (the balance of the circuit being considered as 



258 



Operating and Testing 



having no resistance) a voltmeter connected across 
from A to B would indicate one volt difference of po- 
tential. If the voltmeter is connected between A and 
C, the resistance between A and C being 5 ohms, the 
voltmeter will show % volt. According to Ohm 's law 
E = IR. I, the current, being constant, the voltage 
between any two points must be proportional to the 
resistance between these tw^o points. If the resistance 
between A and D is one ohm, the voltmeter connected 
between A and D would indicate 1/10 volt, while if 
the voltmeter was connected between B and D it would 
indicate 9/10 volt. The resistance of the wire A B 

B 



iTWVWWWVi 



D 



y 



Figure 161 

might be 20 or 30 ohms, or the battery might have a 
voltage of 10 or 20 volts, the drop over any two points 
on the resistance would, nevertheless, be proportional 
to their resistances. 

In Figure 162, two resistances are connected in par- 
allel wdth each other, and in series with the battery. 
If the voltage of the battery is one volt, that difference 
of potential will be shown by a voltmeter connected 
across A and B. The difference of potential between 
A and any point in the resistance A C B will be pro- 
portional to the resistance over which the voltage is 
measured. The same is true of resistance A D B so 



Instruments for Testing 



259 



that for every point in wire A C B there is a corre- 
sponding point in resistance A D B of the same differ- 
ence of potential. Suppose C and D to be two points 
of equal potential, then there would be no current flow 
over a wire connecting these two points, and a galva- 
nometer placed in this wire would indicate nothing. 
The resistance of A C will then be to the resistance of 
B C as the resistance of A D is to the resistance of 
D B. or calling these resistances b, x, a and r respect- 




lAMAA/WWV- 



\ 



Figure 162 

ively we have the proportion a -f- r 
pression may be written 



X. This ex 



— == — , then x = — r 
r X a 

A diagram of the connections of the Wheatstone 
bridge is shown in Figure 163, a and b are the pro- 
portional arms, while r is the known resistance and x 
the unknown, or the resistance to be measured. The 
battery is connected across A and B while the galva- 



260 



Operating and Testing 



nometer is connected between C and D. Both battery 
and galvanometer circuits are provided with keys and 
are normally open. 

In the type of bridge shown, the resistances are con- 
nected between brass strips, brass plugs inserted in the 
holes between the strips short circuiting those resist- 
ances which are not used. In each of the proportional 
arms a and b one plug is always left out. 

To measure an unknown resistance, proceed as fol- 
lows: Connect the resistance to be measured across 
the terminals at X. Leave unplugged one resistance 




Figure 163 

in each of the arms a and b. If it is known that the 
resistance of the apparatus being measured is not less 
than the smallest resistance in r or greater than the 
greatest resistance in r, make the unplugged holes in 
a and b of equal resistance, say 10 and 10, and remove 
one of the plugs in the arm r. Now press down the 
battery key and then the galvanometer key and note 
the direction of the deflection of the galvanometer 
needle. Now either replace or remove some of the 
plugs in r and proceed as before, and note the deflec- 
tion. If the deflection is in the opposite direction the 



Instruments for Testing 261 

value of the unknown resistance must lay somewhere 
between these two, and if the deflection is in the same 
direction as before, note the extent of the deflection, 
if greater tuo much resistance has been plugged in and 
if less, too little. Repeat these operations until no 
deflection is obtained. The total amount of the un- 
plugged resistance in r will then be equal to the re- 
sistance being measured, for 

b b 10 

X = — r, where — = — 1 
a a 10 

If the resistance or the apparatus being measured is 
such as not to come within the limits of the resistance 
in arm r, the unplugged resistance in one of the pro- 
portional arms a and b must be varied. If x is large 

b 
as compared with r, then from the formula x =: — r 

a 

we see that b must be made greater than a. If 10 ohms 
is unplugged in the a arm and 100 ohms in the b arm, 
then the unknown resistance x will be 100/10, or ten 
times the resistance in r. On the other hand, if x is 

b 
small as compared with r, then — must be small. With 

a 

ten ohms unplugged in b and 100 ohms in a, x would 
be 10/100, or 1/10 of r. 

When balance is obtained, the position of the battery 
and galvanometer could be reversed without changing 



262 



Operaiutg ajtd Testing 



the indication of the galvanometer. In using the 
bridge the battery key should always be depressed 
first, for in measuring a resistance containing induct- 
ance or capacity such as a long lead covered cable or 
a circuit containing magnets, if the galvanometer key 
is depressed first and the battery key afterward, a 
deflection might be obtained on the galvanometer even 
with the resistances balanced, this being due to the 



:\/ V| ; v' V! ;V Vj ;v^ V ; 




Figure 164 



factjthat inductance or capacity in the circuit tend to 
momentarily hold back the current so that it requires 
sonie time to come to its full value. 

One form of Wheatstone bridge known as the Queen 
Acme testing set, which is in very common use, is 
shown in Figure 164 with a diagram of connections 
shown in Figure 165. A galvanometer and battery 
form a part of this set so that the instrument is com- 
plete in itself. A number of round brass blocks 



Instruments for Testing 



263 



mounted on a hard rubber base form the terminals of 
the various resistance coils, as shown in Fi^re 164. 
Brass plugs inserted in the openings between these 
blocks short circuit the resistance coils so that only 
those coils are in use on which the plugs are removed. 
The middle row of blocks form the two proportional 
arms corresponding to A and B, Figure 165, while 
the upper and lower arms form the resistance R. 
The resistance to be measured is connected between 




,.'.^.^'% 



Figure 165 

the posts marked X. The battery circuit is normally 
open, being closed by the key B. The galvanometer 
key is also normally open, being closed by the key 
marked G. When this latter key is released it makes 
contact with the point shown above the key, this short- 
circuiting the galvanometer winding. This action 
tends to stop the swinging of the needle and makes it 
come to rest quickly. Six chloride of silver cells are 
provided in a sealed metal case. Connection is made 



264 Operating and Testing 

to the cells by means of small plugs fitting over pins 
which are connected to the separate cells. By this 
means the battery strength can be varied for various 
tests. 

The galvanometer is of the permanent magnet type, 
having a movable coil. 

One particular feature of this bridge is the method 
of reversing the proportional arms A and B. This is 
more clearly shown by reference to the diagram, Fig- 
ure 165, which shows a simplified diagram of the con- 
nections of the bridge. The two proportional arms are 
provided with different resistances, A having 1, 10, 
and 100, while B has 10, 100, and 1,000. With the 
plugs inserted between A and R and B and X arm 
A is placed in series with R and arm B with X. The 
resistance of X will now be 

B 
X = — E 

A 

With the plugs placed in the other two holes, be- 
tween R and B and A and X the above arrangement 
is reversed or 

A 

X = — R 
B 

With the lowest resistance in A, 1 ohm, and the 
highest resistance in B, 1000 ohms X will be 1000 
times R for the first positon and 1/1000 of R for the 
second position, so that for measurement of high re- 
sistances the plugs should be placed as shown in the 



Instruments for Testing 265 

diagram, while for measurement of low resistances the 
plugs should be placed in the opposite noles. With a 
single plug inserted between R and X, the instrument 
may be used as a straight resistance box, the connec- 
tion being made between the posts X. 

MAGNETO 

The magneto is used for testing purposes w^here an 
approximate determination of the insulation resist- 
ance or a test as to continuity of a conductor is de- 
sired. This piece of apparatus is a simple form of 
alternating current dynamo. The fields are formed by 
permanent steel magnets, while the armature is made 
of soft iron, the wires being wound through two slots 
running parallel with the axle. The armature wind- 
ing consists of one coil of a considerable number of 
turns of fine wire. One end of this coil is directly 
connected to the metal frame of the magneto, while 
the other end is connected to an insulated pin running 
through one end of the shaft. 

By means of a crank connected to a gear wheel work- 
ing in a pinion on the end of the armature shaft, the 
armature is turned at a high speed. As the armature 
revolves an alternating current is generated flowing in 
one direction during half a revolution of the armature 
and in the reverse direction during the balance of the 
revolution 

A polarized bell is connected in series with the mag- 
neto armature. A ring may be obtained with the ordi- 
nary testing magneto through a resistance of from 
25,000 to 50,000 ohms, the capacity of the magneto de- 
pending on the strength of the permanent magnet, 



266 Operating and Testing 

number of turns of wire on the armature and the speed 
at which the armature is revolved. 

In testing lead covered wires or cables, a ring is 
sometimes obtained even when the line which is under 
test is clear. This effect is due to the lead covering of 
the cable which causes it to act as a condenser, becom- 
ing charged as current from the magneto flows into 
the wire and then discharges back through the bell 
magnets. The same effect may be produced in testing 
lines installed in iron pipe. In this case the action is 
as follows: When current from the magneto flows 
into the wire lines of force are produced in the space 
around the wire, these lines of force being greatly in- 
creased by the presence of the iron pipe. As the cur- 
rent ceases to flow into the pipe these lines of force 
close in on the wire and produce a current in the op- 
posite direction to the original current. 

These effects are generally obtained on long runs of 
wire only so that for the ordinary test the magneto 
will indicate correctly. 

TELEPHONE RECEIVER 

One of the most convenient devices for ordinary 
testing purposes consists of a telephone receiver con- 
nected in series with a few cells of dry battery. An 
outfit of this kind is easy to make, and has the advan- 
tage of being small and easy to carry about. The out- 
fit generally consists of what is known as a ^Svatch 
case" receiver connected to two small cells of dry 
battery. Flexible cords of suitable length are pro- 
vided with clips at the ends. A permanent connection 
can be made with one terminal and the other used for 



Instruments for Testing 267 

testing. The outfit is very light and can be easily car- 
ried in the pocket. 

This apparatus has several advantages over the 
magneto. A test can be made in much less time as the 
necessity of turning the magneto is avoided. The tel- 
ephone receiver being more sensitive than the magneto 
bell, the approximate resistance can be more readily 
ascertained. In fact, with a little practice one may 
become so accustomed to the ^^ click'' as to be able to 
determine very closely the insulation resistance. In 
using the apparatus in this way, contact should be 
made by simply ''tapping'' the wire which is being 
tested. The connection should never be left on for 
any great length of time, as the battery will weaken 
and the click will be reduced. 

In testing for insulation resistance with a magneto, 
or in fact, any of the common methods in use for this 
purpose, the condition of perfect insulation is shown 
by no indication on the testing apparatus; for in- 
stance, no ring with the magneto. The same indica- 
tion would be obtained if the apparatus was defective, 
or if the wires connected to the apparatus were broken 
so that one is never certain when no ring is obtained 
on the magneto bell that the wire being tested is 
clear. 

With the battery and receiver a click will be ob- 
tained on nearly all tests, even though the insulation 
resistance is very high so that one can always be sure 
that the apparatus is working properly. 

In testing a lead covered cable or wires in conduit, 
the condenser effect due to the lead covering will cause 
a click even where the wire which is being tested is 



268 Operating and Testing 

clear. This may be overcome by making a succession 
of contacts, the first contacts charging the lead cover- 
ing and the succeeding contacts indicating the condi- 
tion of the wire. 

In making up an apparatus of this kind, it is well to 
have some means of opening the battery circuit when 
not in use, so that the battery will not short in case 
the ends of tLe flexible cords should come together. 



CHAPTER XIX 

TESTING DYNAMOS AND MOTORS 

The usual tests to be made on dynamos are : 
Insulation resistance. 
Eise of temperature. 
Regulation.. 
Efficiency. 

The insulation resistance is easily measured by a 
voltmeter attached to a circuit, as shown in Figure 166. 




Figure 166 

If there is any indication of current, the insulation is 
defective. The voltage used for this test should be 
equal to that for which the dynamo is intended. Very 
often such an indication is due to dampness and the 
machine may be cleared up by running it for a while 
w^ith a strong current that will cause the wiring to 
heat up considerably. This must not be attempted if 
the voltmeter indicates a serious defect. 

269 



270 Operating and Testing 

The formula for use in connection with a voltmeter 
when the exact amount of the resistance is desired to 
be known, is : 

V — V 
X = R 



V 

Where V is the full voltage of battery or other 
source of current and V the reduced reading obtained 
through the voltmeter and the resistance to be meas- 
ured, and R the resistance of the voltmeter. 

To determine the temperature rise, the machine 
must be run for some time with the full current for 
which it is designed. Small machines often attain 
their maximum temperature in five or six hours, 
larger ones must be run longer. It is always advisable 
to continue the test as long as there is any noticeable 
increase in temperature from time to time The test 
is made by placing a suitable thermometer upon the 
frame of the machine and covering it with waste so 
as to eliminate the cooling influence of the air. As 
an undue rise of temperature causes the most harm to 
the windings, it is to these that the thermometer 
should be applied and in such a location that the high- 
est temperature produced in any accessible place will 
be recorded. 

Roughly a temperature rise of about 60 degrees 
above the surrounding atmosphere may be allowed but 
if the machine is to operate in a very hot room, a lesser 
allowance must be made. Very few insulations will 
stand a temperature higher than 150. 

To test the regulation of a machine it should be 



Testing 271 

run with loads varying from to the full load. The 
greater the drop in voltage within these limits, the 
poorer is the regulation of the machine. If a com- 
pound wound machine is to be tested in this manner, 
the compound winding must be short circuited so that 
it will have no effect upon the voltage. After the fore- 
going test has been made, the compound winding may 
be placed in service and another test made to deter- 
mine the regulation with this winding in action. 

While this test is being made the action of the com- 
mutator may also be noted. A change in load, of 
course, brings with it a necessary change in the posi- 
tion of the brushes. This should not be very much, 
however, as the machine will be troublesome to 
handle. 

The regulation test with motors is simply a test for 
variation in speed with changes in load. The load 
may be placed upon the motor by means of the Prony 
brake arrangement, shown in Figure 168, or by ar- 
ranging to have the motor drive a dynamo as illus- 
trated in Figure 167. In this test the change in volt- 
age of the line supplying power should be taken into 
consideration. If there is much resistance in this line 
there will be considerable drop in voltage and this will 
cause a slackening off in speed. 

A well designed shunt motor at the terminals of 
which a constant E.M.F. is maintained should not 
drop off more than 10 per cent in speed from no load 
to full load. 

Figure 167 shows the connections for testing dyna- 
mos and motors without the expenditure of much en- 
ergy. The motor M drives the generator G and the 



272 



Operating a)id Testing 



current from it is pumped back into the line. The 
actual energy absorbed and lost in the test is only that 
which is taken up to overcome the friction and the 
losses in the two machines. This arrangement for ob- 
taining a load can be used for any of the tests previ- 




Figure 167 

ously described. The power consumed by the two is 
found by multiplying the volts and amperes used by 
the motor. 

The power delivered back to the line is equal to the 
product of the volts and amperes in the generator cir- 



Testing 



273 



cuit. Roughly the efficiency of the two is the load on 
the dynamo divided by the power delivered to the 
motor. 

In order to obtain the efficiency of the generator, 
we must first have the efficiency of the motor. If the 
two machines are similar, either motors or generators 
it will probably be accurate enough to assume that 
half the loss occurs in each machine. 

If such is the case, we must take the square root of 
the combined efficiency to obtain the efficiency of the 





Figure 168 

single machines. Thus, if the efficiency of the two ma- 
chines is .81, the efficiency of either machine singly 
Avill be .90. 

The efficiency of a motor may be tested by means 
of the well known Prony brake shown in Figure 168. 
In this figure P is a pulley attached to the shaft of 
the motor. The lever L is fastened to the pulley by 
means of the block and the thumb screws. When 
the motor is in motion the screws must be so tight- 
ened that they will allow of rotation of the armature 
shaft sufficient so that the motor may be taking the 
current at which it is to be tested. The spring scales 



274 Operating and Testing 

are provided to measure the force with which the 
motor acts upon the lever. 

In order to learn the power delivered by the motor 
we must know the length of the lever from the center 
of the pulley to the scale. The number of pounds reg- 
istered on the scales and the speed of the pulley in 
revolutions per minute. The product of these factors 
divided by 33,000 will give us the H. P. delivered by 
the motor. 

The products of the volts and amperes maintained 
at the terminals of the motor while the foregoing ob- 
servations were made will give us the H. P. consumed 
by the motor and the H. P. delivered divided by the 
H. P. consumed w^ill give us the efficiency of the mo- 
tor. 

In connection with alternating current motors the 
volts and amperes at the terminals of the motor must 
be multiplied by the power factor. The power factor, 
however, varies with the load on the motor and other 
line conditions and will generally have to be guessed 
at unless a power factor indicator is at hand. 

The above test is usually made at full load. If the 
losses at no load are required we need but take the 
produce of the volts and amperes when the motor is 
running empty. 

The loss in the fields of a dynamo or motor may be 
made exceedingly small or may take up nearly the 
whole output of the machine. From time to time 
cheap motors are brought out that require almost as 
much energy to excite their fields as is required to do 
the work. A test of the field losses can readily be 
made by measuring the current flowing in them. This 



Testing 275 

should not be mneh over 5 per cent of the capacity of 
the motor for medium sizes. 

CIRCUIT TESTING 

Figure 169 can be used to illustrate the principles 
which underlie the testing for trouble on series arc 
or incandescent circuits. The principal troubles en- 
countered on such circuits are due, either to an open 
circuit, or to one or more grounds. If more than one 
ground exists and if those grounds are ''good," they 
will cut out a number of lamps and for that part of 
the circuit amount to the same thing as though a 
short circuit existed on a multiple circuit. If, for in- 



A\ 
7i\-^ 



Figure 169 

stance, two good grounds exist as shown at B and C, 
they will have the effect of cutting out the lamps 
sho\\Ti at the right, the current passing through the 
low resistance of the ground rather than through the 
lamps. 

Sometimes, however, such grounds are not very 
good and then they merely rob the lights of part of 
the current; at other times such grounds are inter- 
mittent and due to wires swinging against wet trees 
or buildings, or the jarring of railroads, etc., which 
cause bare parts of the wires to come in contact with 




/imp; ^i^ 









276 Operating and Testing 

grounded parts of structures. So long as there is 
but one ground on a system no harm can result be- 
cause this can establish no circuit through which cur- 
rent can flow. But when the second ground appears, 
there is sure to be trouble, and furthermore the ex- 
istence of one ground makes the appearance of a sec- 
ond far more likely because the resistance from pole 
to pole through the ground is thereby reduced one- 
half. 

If one ground exists, the repair man or operator, if in 
connection with the ground will, when he touches the 
wire, at once establish the second ground and cause 
more or less current flow through his body. It is, 
therefore, of the utmost importance from every point 
of view to detect grounds as soon as they come on to a 
system. For this purpose every plant should be 
equipped with a ground detector as elsewhere described 
and frequent tests should be made with it. 

If a ground has been noted on the line, the best way 
to locate it is the following : Cut off the current, leave 
the circuit open, and place a temporary ground on one 
of the wires at the station ; then go out along the line 
and at some convenient place open the circuit of that 
wire on which the temporary ground is placed. In- 
sert into the circuit any of the testing instruments 
previously described. So long as an indication is ob- 
tained it shows that you have cut into the circuit be- 
tween the two grounds ; when no further indication 
can be obtained the ground has been passed ; thus, sup- 
pose the ground to be located is at B, Figure 169, and 
the temporary ground at A; if the testing set is in- 
troduced at D, there will be an indication of current, 



Testing 277 

while when it is placed at E there can be none. If 
the line has been closely watched, it is very unlikely 
that more than one ground will come on suddenly but 
in case of an old line that has been neglected and in 
the event of a heavy rainstorm, it may be possible 
that several grounds appear together. If the condi- 
tions make this appear as likely, it will be well to cut 
the line into sections and see which parts are clear 
as the above test will be very confusing if more than 
one ground should exist at the same time. 

If the line cannot be cut dead long enough to locate 
the ground, there are two ways in which the ground 
can be located. One method which may be used if the 
ground on th3 line is good and if there is no danger 
from fire, consists in putting a second ground onto 
the system and noting which lamps are thereby cut 
out of the circuit. Thus, if as in Figure 169 the 
ground to be located exists at B and a test ground is 
put on at A, all of the lamps between A and B will 
be cut out and will show that the ground is somewhere 
between the two lamps, on either side of B. 

In place of the foregoing, connections may be made 
as shown in Figure 169, at the left. Here the little 
circles represent a series of 100-volt incandescent 
lamps (each lamp requires twice the voltage of one 
of the arcs) , which by means of the throw over switch 
S may be connected to either side of the circuit. G is 
a ground permanently connected at the last lamp in 
the series. These lamps as connected virtually meas- 
ure the difference of potential which exists between 
the point on the line at which the ground is located 
and the location of the ground at the lamps. If, with 



278 Operating and Testing 

a ground located at B, connection is made by the 
throw over switch to the positive wire, there will be 
only the difference of potential due to four lamps 
which will cause the incandescent lights to bum, while 
if connection is made to the negative wire there will be 
a difference of potential equal to eleven arc lamps 
which will manifest itself on the incandescent lights. 
By means of the flexible wire shown in dotted lines, 
some of the lamps can be cut out until those remain- 
ing in circuit burn at full candlepower. If the volt- 
age of the incandescent lamps is as indicated above, 
twice that of the arcs, then for every incandescent 
lamp burning at its proper candlepower, there will be 
two arc lamps between the station ground and the one 
on the line ; in the case as shown in diagram, if con- 
nection is made to the upper wire, two incandescent 
lamps will burn properly while with connections made 
to the lower wire, five will bum. 

To locate open circuits it is also of advantage to 
place a ground on one side of the line, at the station 
as at A. Now go out on the line and test back to this 
ground, of course, grounding the instrument you have. 
As long as you are located between the open place and 
the station, you will get an indication ; when this place 
is passed no further indication can be obtained. 

In connecting up arc lamps, it is best to begin at 
one end of the circuit, determine whether this is to be 
positive or negative, and connect the first lamp accord- 
ingly. Now ground that end of the circuit and pro- 
ceed to the next lamp on that leg. If the wires are 
run overhead, there will be no difficulty in tracing the 
wires, but if they are underground there will be two 



Testing 279 

ends visible, and it must be determined which of these 
is to go to the positive and negative poles of the lamp. 
By grounding the end from which the start was made 
it will be easy to test back and find the leg which 
comes from the lamp first connected. 

The finding of grounds on multiple circuits is a 
much simpler matter. Such systems are always sub- 
divided into branch circuits so that no great amount 
of wiring is ever dependent upon a single fuse, and 
by these fuses any part of the weiring can be readily 
separated from the rest. A ground having been dis- 
covered on such a system, it becomes necessary to dis- 
connect different centers until the one containing the 
ground is found. "When so much is accomplished the 
branch circuits are next disconnected until the proper 
one is found. After this, if the wiring is open, an in- 
spection will reveal the exact location, if the wiring 
is concealed it may further be necessary to disconnect 
parts of the circuit until at last the section containing 
the trouble is found. 

With multiple circuits a broken wire always indi- 
cates very nearly its exact location, so that it can eas- 
ily be found by inspection. If, for instance, in Fig- 
ure 170, the wire is broken at E, the seven lights at 
the right will not burn, while those at the left will not 
be interfered with; if only the wire at F is broken 
only one light will be out. 

A new system of incandescent lighting is best tested 
circuit by circuit. By testing for ground over a 
whole installation at once, there is always the chance 
that some of the fuses may not make proper connec- 
tion (especially with cartridge and plug fuses) there 



280 Operating and Testing 

is also a likelihood that some of the switches may be 
left open; either of these conditions would make the 
test very unreliable. AYhen each circuit is tested by 
itself the testing instrument can be connected to the 
binding posts of the cut-out, or at any socket in the 
circuit, wherever it is most convenient to obtain a 
ground connection for the instrument. Unless lamps 
are installed in the sockets each leg must be separately 
tested, and if switches do not indicate Avhether on or 
off, the test should be made with the switch in two po- 
sitions, one of which is sure to be on. AVith most snap 
switches it is, however, easy to determine by the 



-^^ 



I I D F 



Figure 170 

sound of the snap whether the switch is closed or open. 

The next test to be made is for short circuit. If a 
good instrument is connected at C and D and a short 
circuit, exists, it will at once cause an indication. If 
there is no such indication, we may proceed to test 
for continuity. For this purpose the testing instru- 
ment may be left at the cut-out and connection made 
at each socket w^ith a screw driver or anything else by 
w^hich the opposite poles can be brought together so 
as to obtain an indication on the test instrument. 
Where plug cut-outs are used, a lamp screwed into 
one of the receptacles of the cut-out is about the only 
test instrument needed except when testing for 
grounds. 

In connection with three wire circuits, it is custom- 



Testing 281 

ary to run the neutral wire in the center, but one must 
not always rely upon this being the case. It is very 
important to have these wires properly connected, as 
a wrong connection will result very likely in the de- 
struction of a large number of lamps, and possibly in 
causing a fire. If the neutral wire on the system is 
grounded there are two ways by which it can be found. 
The simplest method, requiring only one lamp, is to 
connect this lamp to ground and to the wires one by 
one, when connected to either of the outside wires the 
lamp will burn at full candlepower, while when con- 
nected to the neutral it will not burn at all. The 
other method requires two lamps but no ground con- 
nection, and on this account is the most used. Con- 
nect two incandescent lamps of the proper voltage in 
series and try the wires, two at a time ; when the posi- 
tive and negative wires are found, the lamps will burn 
brightly, while in connection with the neutral they 
will be at less than half candlepower. This test is 
also often made by touching the w^ires with the fingers 
where the voltage is not over 220 and determining by 
the severity of the shock which are the two outside and 
which the neutral wire. 

If it is desired to learn which is the positive or neg- 
ative wire, the test can be made by inserting ends of 
wire connected to the two poles of the circuit through 
some water contained in a small cup (non-conducting 
material preferred). The negative pole will be indi- 
cated by the formation of small bubbles of hydrogen 
gas near the wire. If a metal cup is used for this test, 
there is, of course, danger of a short circuit if the 
wires come in contact with the metal. 



282 Operating and Testing 

In Figure 171 we explain the testing out for the 
connection of a pair of three-way switches. It is as- 
sumed that the wires are run in conduit and nothing 
but the ends of the wires in the three junction boxes 
are visible. The switches are to be located at 1 and 2 
and the lamp to be controlled by them at 3. First find 
which are the feed w^ires, in this case 4, and bend them 
out of the way ; now at each of the switch outlets take 
any two of the three wires and twist the bared ends 
together and proceed to the light outlets, and by test- 
ing find the two short circuits thus made and perma- 
nently connect these two sets of wires together. Con- 



-4 



Figure 171 

nect the lamp to the remaining pair at this outlet and 
at 1 connect the single wire coming from 3 to one of 
the feed wires. The remaining feed wire now goes 
to that pole of the switch which is in direct connec- 
tion w^ith the line, and the other two are connected to 
the other binding posts. The other switch outlet is, 
of course, connected in the same way. 

Figure 172 will help to illustrate the method of 
testing out a circuit of incandescent lighting for the 
purpose of making the final connections. We begin 
by placing some testing instrument and battery at the 
cut-out and connecting it to the circuit as at T. Now 
proceed to one of the outlets and baring the ends of 
wires found there, bring the different ends temporar- 



Testing 



283 



ily together until two wires are found that cause an 
indication on the testing instrument. The most con- 
venient instrument for this purpose is an ordinary 
call bell and battery, as it can be heard throughout 
different rooms. After the wires coming from the 
cut-out have been found, ends at other outlets may 
be temporarily connected together as, for example, at 
L and we now again try different Avires in connection 
with the pair found until a ring is obtained \^kich in- 




Figure 172 



dicates that we have found the wires thus connected 
together. In this manner by proceeding from outlet to 
outlet the meaning of every wire can be determined 
and connections made as required. As a precaution, 
before beginning to test out in this manner, it will be 
well to separate all wire so there may be no accidental 
short circuits, which would cause confusion. 

Three tests should be made on every fixture before 
it is installed, and for these tests sensitive instruments 
should be used, or a voltmeter and the pressure of the 
lighting system. The first test may be for short cir- 
cuit in the wiring and for this purpose connections 



284 Operating and Testing 

are made as shown in Figure 173. If this test shows 
clear the connections may be left as they are and a 
test for continuity made by inserting a screw driver 
or other piece of metal into each socket so as to com- 
plete the circuit through the voltmeter and cause an 
indication. If all sockets are found perfect, the test 
for contact wnth the metal of the fixture may be made 
by disconnecting one of the wires, say 3, and bringing 
it in contact with the metal of the fixture while the 




Figure 173 

disconnected fixture wire is connected to the other 
wire of the voltmeter at 2. 

A circviit can be tested for loss in the following man- 
ner: With a voltmeter measure the voltage at the 
supply end of the line, and also at the center of dis- 
tribution or at the motor, as the case may be. The 
reading will always be greater at the supply end and 
the difference between the two will be the loss in volt- 
age. In order to find the percentage of loss in the line, 
we divide the volts lost by the volts at the supply end. 

The loss varies with the current and is inversely 



Testing 285 

proportional to it. In order, therefore, that the test 
may be of value, it must be arranged that at the time 
of test the average current be in use or if this is not 
practicable, the current flowing at the time of test 
must be known. The average loss will be in the same 
proportion to the loss indicated as the average current 
is to the current flowing at time of test. This cur- 
rent multiplied by the volts at the supply end of the 
line, will give the total watts delivered at this point, 
and this multiplied by the percentage of loss will give 
the total watts lost. 

Instead of making the above test with a voltmeter, 
it can be calculated if the size of the wire used is 
known. The loss in voltage is equal to the current 
multiplied by the resistance, and, therefore, if the re- 
sistance is known, we need but multiply with the am- 
peres to find the loss in volts. In the table below the 
loss in volts per 100 ampere feet (length of run, one 
leg, X current) is given to facilitate those calcula- 
tions. The loss in volts is the same, no matter wliat 
the voltage of the system may be but, of course, the 
percentage of loss which the actual loss represents 
differs with the voltage of the system ; thus, a loss of 
51/2 volts corresponds to a loss of 5 per cent at 110 
volts, but only 21/0 at 220. 

Loss in volts 
B. S. gage. per 100 amp. ft. 

14 53 

12 33 

10 21 

8 13 

6 08 



286 Operating and Testing 

4 052 

3 04 

2 03 

1 026 

02 

00 016 

000 013 

0000 .01 

To find the loss in any line by the use of this table ; 
multiply the current by the length of one leg of the 
line and divide by 100. Use the product so obtained 
to multiply the loss given in the table, the result will 
be the total loss in volts in the line. 

If the size of wire in any installation is not kno\\TL, 
the best and simplest manner wherever practicable 
to determine it is with a wire gage. Such a gage is, 
however, not always at hand and in connection with 
wires already installed, often cannot be used without 
cutting into the insulation. 

Below is given a table by which the gage number 
of wires can be quite approximately determined from 
outside measurements. Although these measurements 
are not perfectly correct, they will not be found suf- 
ficiently inaccurate so that any very great errors will 
be caused thereby. 

The circular mils contained in any wire can be 
found by multiplying the diameter of the wire ex- 
pressed in thousands of an inch by itself. If the wire 
in question is stranded, the square of the diameter 
must be multiplied by .75, this will give quite approx- 
imate results although not quite accurate. 



Testing 



287 



xn 

m 
I— I 

O 

PC! 

<1 



t— ( 

o 

o 

I— I 

o 
w 

I-:] 
fQ 



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TESTING FOR, AND PREVENTION OF ELECTROLYSIS 

The damage due to currents of electricity passing 
from the grounded part of the structure and rails of 
any system of distribution, such as a street railway 
line for instance, depends entirely upon the relative 
resistance of the metallic return circuit afforded by 
the structure and whatever auxiliaries may have been 



288 Operating and Testing 

provided and the resistance of the earth in the vicin- 
ity of the structure. 

There are but two ways in which this action can be 
lessened or prevented, the insulation of gas and water 
pipes being considered impracticable One of these 
methods consists in providing a metallic return cir- 
cuit of very low resistance so that only a very small 
amount of current wdll escape from it. With this 
method the amount of copper required is large and 
varies with the conductivity of the earth return in 
different places. At best it can only mitigate the evil 
since no amount of copper can ever entirely prevent it. 

The other method consists in bonding all pipes and 
other metallic bodies that are underground in the 
vicinity of the structure to the structure in such a 
way that current can pass to and from them without 
doing any damage. This latter method, of course, in- 
volves also the bonding of all pipes at all joints. If 
this is not done, it will aggravate the trouble rather, 
than lessen it, since the various bonds might conduct 
a large quantity of current to a certain pipe w^hich 
might be a very good conductor with exception of one 
joint, for instance, and at this joint the greater part 
of the current would pass from the pipe to earth and 
back again, thus rapidly causing serious damage. All 
of the damage occurs where the current leaves the 
pipes, and if it is not possible to make the piping a 
part of the return system as above described, the next 
best thing will be to protect those points where the 
current leaves the pipes. 

To determine how this can best be done, comprehen- 
sive tests should be made. With a voltmeter which 



Testing . 289 

will indicate the direction of the current, readings 
should be taken at a number of places, the more the 
better, from the structure or rails to accessible parts 
of gas and water pipes near the structure. The pres- 
sure and direction of current should be noted so that 
complete map of the system can be made from it. This 
being done, a map of the piping along the line of the 
railway should be provided, and the two combined in 
such a way as to show the exact relative position of 
pipes and leaks. In addition to this careful tests of 
the bonding of the structure should be made, and any 
bad spots marked upon the map. The map will now 
reveal quite approximately the relations existing be- 
tween the structure and the earth, pipes, etc. The 
current flowing between structure and piping cannot 
be measured, but may be estimated. 

If high pressure towards a pipe is found to exist 
and at the same time the pipe is very close to the rails, 
it would indicate a large current. The same pressure 
with the pipes farther away would suppose a smaller 
current. Again the high pressure might be caused 
by one or a few bad bonds. If the structure is 
perfect, and the pipe lines are also in about the same 
condition throughout the route, a maximum pressure 
from the rails to pipes will be found at the far end, 
and this will gradually decrease toward the middle 
and will from there on be in the opposite direction, 
from pipes to rails toward the power house.' No atten- 
tion need be paid to current passing from the rails. 
The endeavor must be to intercept the current where 
it leaves the pipes, especially where large currents are 
indicated. Unless the pipe line can be bonded through- 



290 Operating and Testing 

out, nothing that would lessen the resistance between 
structure and pipes should be installed, because this 
would increase the current. It would, therefore, seem 
to be advisable to connect suitable ground plates to 
the pipes where current leaves them, so that the elec- 
trolytic action would take place on these instead of on 
the pipes. If, however, the pipes are very close to 
the rails, the bonding to the structure would not af- 
fect the total resistance of the earth return much, and 
would, therefore, be preferable. In many places cur- 
rents will be at different times found to be in different 
directions, so that all tests should be made to extend 
over some time. 



* 



F 



G 






Figure 174 

With conditions as shown in Figure 174, where the 
bad bond is indicated near the pipe, a train using cur- 
rent at G would cause current to flow from the rail 
to the pipe at the far end and from pipe to rail at the 
left of the bad bond. A train using current at F would 
cause a flow of current in the opposite direction. So 
long as the pipe is near the rails, it will always receive 
som.e current. 

Tests should be made during that part of the day 
when the load is most evenly distributed. This will 
be at the busiest time. The pressure will vary with the 
currents used in the vicinity at time of testing. The 



Testing 291 

voltmeter used in testing is connected from the rails 
to the pipe. It is preferable to have a double scale 
voltmeter, which will also indicate the polarity, but 
this is not essential. If no reading is obtained at a 
certain place, with the wires connected one way, they 
may easily be reversed and the polarity noted on the 
map. 

In Figure 175 a common method of testing bonds is 
illustrated. An ordinary milli-voltmeter is used and 
about 50 feet of No. 20 wire are inserted in each of the 
leads, as indicated in the diagram. This will give a 
resistance of about % ohm. The two wires nearest 




Figure 175 

the voltmeter in the diagram are permanently fast- 
ened to bridge the bond, and the other wire is moved 
back and forth on the adjoining rail until a spot is 
found at which the voltmeter gives no indication while 
current is flowing. The resistance of the bond is now 
equal to the resistance of the length of rail between 
the other two wires. If any bond shows up much worse 
than the others, it should be attended to. 



PHOTOMETRY 



To measure the efficiency and the candlepower of 
different electric lights is a simple matter and much 
more attention should be given to such measurements 
than is usually accorded them by operators in charge 



292 Operating and Testing 

of illuminating stations. Thousands of dollars worth 
of fuel is wasted annually because owners and opera- 
tors do not understand the loss of energy caused by 
continuing lamps of low efficiency in service. 

There are two very simple methods of measuring 
candlepower ; one of these is known as Rumford's, and 
is illustrated in Figure 176. A suitable pencil is set 
up about 2 inches from a wall of light color or a simi- 
lar screen. A standard lamp is set up a convenient 
distance from this pencil, so as to cause a shadow from 
it to fall upon the screen. The lamp to be tested is 




Fiorure 176 



'G 



then set up in such a manner as also to cause the pen- 
cil to cast a shadow upon the same screen but at a 
different angle from the other. It will be noted that 
each lamp illuminates the shadow made by the other 
and that when the intensity of the two lights at the 
screen is equal, the shadows will be of equal darloiess. 
The lamps must be adjusted at such distances from 
the screen that both shadows are equal. The candle- 
power of the two lamps is now proportional to the 
squares of the distance that each is from the screen. 
If one is 32 inches from the screen while the other is 
23, the candlepower of the farther lamp is to that of 



Testing 



293 



the nearer as 1024 is to 529, or nearly twice as great. 
In order to make this test as sensitive as possible it is 
best to move one of the lamps backward and forward 
in such a way as to be sure that it is a little too far 
in one positon and then a little too close in the other 
and then place it finally in an intermediate positon. 

To measure the power consumed by each of the 
lamps an ammeter and a voltmeter are necessary. If 
connected as in Figure 176 the voltage of both lamps 
will be the same. The current consumed by each lamp 
can be gotten by removing one lamp at a time from 
the circuit, thus requiring only one ammeter. The 
efficiency of the lamp is usually expressed in watts per 



' M I ' 1 1 M M I M ' I ' I ' 1 ' ' ' I ' ' ' I ' ' ' I ' I 



I ' 



TTT 




Figure 177 

candlepower. If ^ ax^ertain lamp yielding 20 candle- 
power is taking 58 watts, there will be 2.9 watts per 
candlepower. 

If lamps are to be tested for use on a certain circuity 
the voltage of that circuit must be applied to them. 
The efficiency and candlepower of incandescent lights 
varies greatly with different voltages. 

Another method, known as Bunsen's, is shown in 
Figure 177. A piece of blotting paper is soaked at a 
convenient place with oil or grease, so as to form a 
small spot. The paper is then placed between two 
lights and moved to such a position that the grease 
spot does not show. When this position is found, the 



294 



Operating and Testing 



illumination on both sides is equal and the candle- 
power of the two lamps are as the square of their dis- 
tance from the paper. 

The illumination obtainable from a lamp varies 
greatly with the angle at which the light is taken, and 
also varies with the shape of the filament. It is fur- 
ther often purposely modified by the use of reflectors. 
In the illumination of desks, halls, etc., it is often im- 
portant to know how a certain lamp or reflector dis- 
tributes the light. For this purpose photometric meas- 
urements must be made at different positions under 



7 I 




Figure 178 

the lamp. This can easiest be done by an arrangement 
outlined in Figure 178. The lamp is fastened to a 
strip of wood hinged at one end so that it can be 
placed in different positions from horizontal to verti- 
cal through a range of nearly 180 degrees. In the po- 
sition shown the light which strikes the pencil or 
grease spot P comes from the tip of the lamp, and is 
the same as would be found directly under the lamp if 
it were hanging. If the lamp is gradually raised 
and the candlepower taken at the different positions 
we can obtain a curve of the illumination throughout 



Testing 



295 



one whole side of the lamp. At each change of posi- 
tion the candlepower must be measured and marked 
off on the radial line in Figure 179 that corresponds 
with the position of the lamp. "When all of these have 
been marked, a curve may be drawn combining them 
which will represent the variation in candlepower. 
Such a curve representing half of the illumination 
from one lamp is shown in Figure 179. For this test 




Figure 179 

the board upon which the lamp lies should be painted 
black, so there may be no reflection. 

When comparative tests are made care should be 
taken that the filaments of the lamps tested are about 
alike. An accurate comparison of different lamps re- 
quires the taking of complete curves as in Figure 145. 
These will give the average candlepower if properly 
figured up (add all of the measurements and divide 
by their sum) and also indicate whether the lamp is 
suited for the place where it is to be used. 



296 



Operating and Testing 



The candlepower of arc lamps is often measured by 
means of the dispersion photometer first suggested by 
Prof. Ayrton. The principle of the arrangement is 
shown in Figure 180. The light from the arc is al- 
lowed to pass through a dispersion lens which spreads 
it out over a greater area and thus lessens its intens- 
ity. ^ 

Since the intensity of light varies as the square of 
the distance it follows that, using a dispersed light, 
we may consider the distance of the lamp from the 
screen as proportional to the square root of the area 




Figure 180 



illuminated by the dispersed light. The lens limits 
the quantity of light, and as it is circular we may 
take the diameter of the circle illuminated as the 
square root of the area. The intensity of the light is 
then the same as though the distance from the arc to 
the screen were equal to D divided by L and multi- 
plied by A ; D being the diameter of the circle of dis- 
persed light, L the diameter of the lens and A the 
distance from the arc to the lens. When the shadows 
cast by the arc and the standard lamp at the pencil P 
are equal, the candlepower of the arc is as much 



Testing 297 



greater as that of the standard I as 



{<) 



is greater than E2. 

Numerical example: Let A equal 24 inches, L 
equal 2 inches, D 18 and E 12 ; we have then 24 X 18 
divided by 2 equals 216 ; this squared equals 46656, 
and this divided by 122 or 144 equals 324, which is the 
relative candlepower of the arc over the standard. 



CHAPTER XX 

DYNAMO AND MOTOR TROUBLES 
DYNAMO TROUBLES 

In this chapter the usual troubles occurring in dy- 
namos are enumerated in the order in which it is most 
likely they occur. As a rule, time will be saved by 
testing for causes in the order in which they are listed. 

FALURE TO GENERATE 

Cause 1. Poor contact of brushes. This in turn 
may be due to dirty commutator, ragged brushes, in- 
sufficient tension on brushes, improper position of 
brushes. A rough commutator, if the dynamo is oper- 
ating at high speed, may prevent contact even though 
at rest the connection may appear to be perfect. 

Cause 2. Open circuit in the fields. In arc dyna- 
mos, this open circuit may be out in the line some- 
where. Poor contact of brushes in series machines is 
equivalent to an open circuit. 

Cause 3, Lack of residual magnetism. Test pole 
pieces with pliers or small piece of iron or steel; if 
there is no attraction, magnetize fields from a battery 
or from switchboard, if accessible. If magnetizing 
with one polarity does not start generation, try mag- 
netizing in opposite direction. Sometimes generation 

298 



Dynamo and Motor Troubles 299 

can be started by striking the pole pieces lightly with 
a hammer. Series dynamos can sometimes be started 
by short circuiting the brushes for a fraction of a sec- 
ond by fastening a wire to one of the brushes or ter- 
minals and wiping the other end across the other 
brush for the shortest possible length of time. 

Cause 4, With shunt dynamos a short circuit con- 
nected to the dynamo will prevent generation entirely. 
With compound dynamos it may do so only to a cer- 
tain extent. There will be some magnetism due to the 
series fields, but none due to the shunt. Disconnect 
everything from the dynamo except voltmeter. 

Cause 5. Wrong connection of half of the fields; 
one opposing the other. This can be tested for with 
a compass. If the fields are right, each will attract 
a dift'erent end of the needle. Do not bring needle too 
close to either pole piece, or it may be reversed in 
polarity. By short circuiting first one and then the 
other it can also be determined whether both field 
coils are acting in the same direction. The needle 
must be attracted the same way, no matter which coil 
is cut out. 

SPARKING OF BRUSHES 

Cause 1. Wrong position of brushes. The brushes 
should be at the neutral point, and this can be found 
by moving back and forth until the point of least 
sparking is found. With increase of load the brushes 
must be shifted in the direction of rotation of the ar- 
mature. When load decreases, the shifting must be 
in the opposite direction. The more modern dynamos 
require very little shifting with changes in load. In 



300 Operating and Testing 

connection with series arc dynamos the sparking at 
the brushes is unavoidable and special appliances are 
usually provided to take care of it. 

Cause 2, Eough commutator, ragged brushes, or 
dirt on commutator. 

Cause 3. Insufficient tension allowing the brush to 
leave the commutator. 

Cause 4. Brush either too narrow or too wide. If 
too narrow it may leave one commutator section before 
making proper connection with the next. If too 
wide, it will short circuit several of the coils and the 
breaking of this current will manifest itself by spark- 
ing. 

Cause 5. Brushes not correctly spaced. In two 
pole machines they should be diametrically opposite 
each other. Except in some special machines they 
should always be equally spaced. 

Cause 6, Changes in load with some dynamos. 

Cause 7. In compound d. c. machines wrong con- 
nection of series coils will ciause sparking. In com- 
pound alternators a wrong setting of the commutator 
will cause sparking. If the load is inductive and 
changing, there must be a constant shifting with 
changes in load to prevent sparking. 

Cause 8, Open circuit in armature. If this is the 
cause of sparking the sparks occur only at one place 
on the commutator and an inspection should reveal 
the location of the break. For exhaustive treatise on 
armature testing and repairing, see ^^ Practical Arma- 
ture and Magnet Wiring." 



Dynamo and Motor Troubles 301 

HEATING OF ARMATURE 

Cause 1, Overload. Compare capacity of machine 
with load. The heating increases as the square of 
the current. 

If several machines are operating in parallel, one 
may be running the other as a motor. With compound 
machines the ammeter m.ay be cut into the same side 
as the equalizer and the reading may be altogether 
unreliable. 

Cause 2.^ Short circuit in armature coil. This will 
speedily show itself by burning out. A strong odor 
of overheated shellac will be the first indication of 
trouble. 

Cause 3. Defective construction; wires too small; 
f oucault currents ; hysterisis. 

Cause 4. Poor ventilation. Some types are ar- 
ranged so they can be either enclosed or opened at 
the ends. 

INABILITY TO REGULATE VOLTAGE 

Cause 1. Speed too low so that even with all re- 
sistance cut out of the regulator the resistance of the 
field circuit is too high to allow sufficient current to 
flow. Fields must be either rewound or connected in 
parallel, and a new suitable rheostat provided. 

Cause 2. Speed too high so that even with all re- 
sistance in circuit the voltage is above that desired. To 
remedy this additional resistance must be provided 
unless, of course, the speed can be made correct. 



302 Operating and Testing 

FIELDS RUNNING HOT 

Cause 1, Voltage at which machine operates much 
higher than intended. 

Cause 2. Fields connected in parallel where they 
were intended to be in series. 

Cause 3, Part of field cut out either by ^ Aground'' 
or improper connection of wires in coil. If this is the 
cause, one of the fields will be abnormally hot and the 
other cool. 

SHOCKS OBTAINED FROM TOUCHING MACHINE 

This is always due to either static electricity or 
grounding of some live part of the system on the 
frame of the machine. Static electricity is caused by 
the belting and can be remedied by providing arrester, 
or the shafting may be grounded. 

To locate ground separate armature and fields and 
test for location. After this, the exact location can be 
found only by inspection and may require unwinding 
of coils. 

SHAFT AND BEARINGS RUNNING HOT 

Improper oiling. Box too tight. Rough bearing 
surface. Bent shaft. Excessive belt tension. End 
thrust due to improper leveling or armature not being 
centered and in consequence possessing a tendency to 
be 'sucked in," thus pressing heavily on one of the 
collars. 

MOTOR TROUBLES 

Fuses blow at starting. 

Cause 1, Fuse may be too small, or contacts may 
be dirty or loose. 



Dynamo and Motor Troubles 303 

Cause 2, Motor may be overloaded, or stuck fast 
in some way. 

Caitse 3, Rheostat may be manipulated too fast. 
As a rule from 20 to 30 seconds should be consumed 
in the starting of the average motors. 

Cause 4, Wrong position of brushes. Brushes 
should be at diametrically opposite points. 

Cause 5, The voltage supply may be higher than 
the motor is designed for. If alternating the. frequency 
of the supply may be lower than the motor requires. 
If the frequency is higher, not enough current can be 
obtained. 

Cause 6, There may be a short circuit in the ar- 
mature or in the field. A short circuit may be caused 
by two grounds in a two-wire sytem, or by one ground 
in three-wire system with grounded neutral. 

Cause 7. The motor may be improperly connected. 

Cause 8. The field circuit may be open, thus pre- 
venting the armature from generating the necessary 
counter E.M.F. 

Cause 9. Light fields, due perhaps to grounded 
wires or short circuit of part of the coils. This will 
be indicated by part of the field running hotter than 
the rest. 

FAILURE TO START 

Fuses do not blow. 

Cause 1. Dead line. Test for current at switch. 

Cause 2. Open circuit in armature or fields, if se- 
ries motor. In armature only if shunt or compound 
motor. 



304 Operating and Testing 

Cause 3, Poor contact of brushes or insuificient 
tension. 

If alternating, frequency of supply may be too high. 
Synchronous motors must be started independently of 
the current. 

SPARKING OF BRUSHES 

See ^^ Dynamo Troubles.'' 

Sparking of motor commutator is often much more 
troublesome than with dynamos, because the load 
changes are more frequent and sudden. Since com- 
pound motors are wound with series fields opposing 
or helping the shunt fields, frequently the sparking 
may be due to wrong connection of the fields 

RACING OF MOTOR 

Cause 1, Series motors require constant regula- 
tion if connected to variable load. If the load is light, 
motor will speed up. 

Cause 2, Light fields due to improper winding, 
grounds, short circuit or improper connection will 
cause any motor to speed up unless heavily loaded. 
Fields intended to be in parallel may be in series. 
Part of the field winding may be connected to op- 
pose the rest. The compound coils may be in opposi- 
tion to the shunt coils. In such a case the speed of 
motor will increase with increase in load until if over- 
loaded the fields will become so light that finally fuses 
will blow. Strength of field cannot be altered by 
adding or removing wire. It must be rewound with 
larger wire, if field is too light, and with smaller if 
field is too strong. i 



Dynamo and Motor Troubles 305 

MOTOR NOT UP TO SPEED 

Cause 1. If series motor, it may be overloaded. 

Cause 2. The line supplying current may be so 
long and the wire so small that with a heavy load the 
speed of motor falls off considerably. This condition 
would not affect a motor running light. 

Cause 3, Fields may be too strong. Fields in- 
tended to be run in series may be in parallel. In 
such a case they will likely run hot. 

FIELDS OR ARMATURE RUNNING HOT 

See ^* Dynamo Troubles." 

MOTOR RUNNING IN WRONG DIRECTION 

Remedy by reversing connections of fields or arma- 
ture. If both are reversed, it will have no effect. As 
long as fields and armature polarity remain in the 
same relation to each other, the polarity of the supply 
line is immaterial. 

Multipolar motors and also some bi-polars can be 
reversed by shifting the brushes so that the negative 
brush takes place of the positive. Three-phase motors 
are reversed by changing any two of the wires. Two- 
phase motors are reversed by reversing the wires of 
one of the phases. 

HEATING OF MOTOR 

Cause 1. Overload. 

Cause 2, Voltage too high. 

See, also, ''Heating," under Dynamo Troubles. 

With induction motors one of the phases may be 



306 Operating and Testing 

out. A three-phase motor will continue to run on one 
phase, but will not start. If such a motor is over- 
loaded, it will come to rest and burn out. 

The above includes all of the common troubles en- 
countered on ordinary motor circuits. Motors are, 
however, used in so many complicated systems of wir- 
ing, as, for instance, in connection with printing 
presses where multi voltage control is often used and 
where motors must be reversible and capable of being 
started or stopped from different places, that the only 
way for an operator to fit himself to deal ^\ith trou- 
bles on such systems is to thoroughly acquaint him- 
self with the details of the wiring. He should draw 
out an accurate diagram of the connections showing 
the location of every wire and learn exactly what its 
purpose is and study this diagram patiently, trying 
out what effect a short circuit at one place or a broken 
or a misplaced wire at another would have. 

By preparing himself in this manner a repairman 
can do in a few minutes what might otherwise require 
hours for, and where the loss due to an idle machine is 
figured at from ten dollars per hour upward, speed in 
locating trouble is of the utmost value. 



CHAPTER XXI 

RECORDING WATTMETERS 

To obtain a record of the amount of electrical en- 
ergy consumed on a circuit in a given time, it is neces- 
sary that some suitable form of instrument be so con- 
nected in the circuit that a continuous record of the 
amount of energy pas^sing over the circuit is recorded. 
The chemical meter, a diagram of which is shown in 
Figure 182, was originally used for this purpose. This 
meter consists of zinc plates suspended in a conduct- 
ing solution, so arranged that a part of the total cur- 
rent used on the circuit passes between these plates. 
At certain intervals the plates were removed and 
weighed, the amount of metal deposited on one of the 
plates showing the amount of current used during 
the interval. 

This meter was in reality a current meter, as it did 
not take into account the variations in voltage on the 
line except, of course, as these might affect the current. 
To reduce the reading to watts it was necessary to es- 
timate the average voltage during the period which 
the meter was in use. Considerable work was en- 
tailed in the ^^ reading'' of these meters, as it was nec- 
essary for the meter man to carry with him enough 
plates to replace those removed and to carry back to 

307 



308 



Operating and Testing 



the laboratory for weighing all the plates removed. 
This type of meter had other disadvantages among 
which was the inability of the consumer to check the 
readings, and the fact that the meter could not be 
used on alternating currents; and they are now en- 
tirely replaced by the mechanical meters. 

It was customary when the chemical meter was in 
use, to show in the monthlv statements sent to con- 




rWWWV 



WVWVW^ 



Figure 182 

sumers the number of lamp hours or the number of 
ampere hours used during the period. The first me- 
chanical meters were simply recording ammeters and 
registered the amount of ampere hours or lamp hours. 
At the present time the wattmeter is used almost ex- 
clusively. 

The ''watt" is the unit of electrical power and is 
the basis of all wattmeter readings. A kilowatt or 



Recording Wattmeters 309 

K. W. is 1,000 watts. An electrical horsepower is 
equivalent to 746 watts. For approximate calcula- 
tions, a horsepower is considered as equivalent to 750 
watts or % of a kilowatt ; likewise a kilowatt is equal 
to 4/3 of a horsepower. A current of one ampere 
flowing through a resistance of one ohm will produce 
one watt, the E.M.F. being in this case, according to 
Ohm's law, one volt. 

E2 

Expressed in symbols W = IE, W = PK, "W = — . 

> R 

An incandescent lamp taking i^ ampere at 110 volts, 
takes % X HO = 55 watts. The same lamp, when 
burning, has a resistance of 220 ohms. The wattage 
is, therefore, according to the formula, W = I^R, 
(1/2)2 X 220 = 55 watte. 

While the ^^watt" expresses the rate at which power 
in an electrical circuit is used, it does not express the 
amount of work performed. To correctly indicate the 
actual work done, the length of time during which the 
power is acting must be taken into consideration. The 
unit of electrical work is the ^^watt hour/' meaning 
that one watt is used for one hour. 

The distinction between a watt and a watt hour is 
similar to the distinction between the speed at which 
a train moves and the distance which it covers. To 
find the distance covered by the train we must multi- 
ply the speed (miles per hour) by the number of or 
fraction of an hour that the train moves at this speed. 
In the same way to get the actual power consumed in 



310 



Operating and Testing 



a circuit, we must multiply the watts consumed by 
the length of time. 

An incandescent lamp taking 55 watts will, in one 
hour, require 55 watt-hours of energy. Ten such 
lamps operated for one hour w^ould require 550 watt- 
hours ; or one such lamp operating for 10 hours would 
require 550 w^att-hours. In a like manner, a horse- 




Figure 183 

power (746 watts) in use for one hour will require 
746 watt-hours. The watt-hour is too small a unit for 
commercial purposes and the kilowatt hour, or 1,000 
watt-hours, is generally used. 

While it will be seen that there is a decided differ- 
ence between the terms ^Svatt" and '^watt-hour,'' 
still it will be found that the two are frequently used 
SATionymously, kilowatt-hours often being referred to 



Recording Wattmeters 



311 



as kilowatts. The connection in which the term is 
used will determine the meaning. For instance, a 
monthly statement referring to so many kilowatts 
must, obviously, mean kilowatt-hours. 

The recording wattmeter, sometimes called inte- 
grating wattmeter, owing to the fact that it indicates 
the total watts used, consists of a small motor operated 
by the current to be measured. Figure 183 show^s a 
view of the Thompson recording wattmeter and Figure 
184 a diagram of the connections. The upright shaft 




Figure 184 

in the center of the meter supports the armature A, 
Figure 184. To reduce the friction to the smallest 
possible amount this shaft rests on jewel bearings. 

The coils of armature A are composed of fine wire 
which terminates in a silver commutator. Brushes, 
lightly bearing on this commutator, convey the neces- 
sary current to the armature. The armature, which 
is connected in series with a non-inductive resistance 
R, and the auxiliary shunt field S, is connected directly 
across the mains. The two field coils M M are wound 



312 Operating and Testing 

with a rather heavy wire and connected directly in 
series with one of the mains. At the lower end of the 
shaft is a copper disk, shown in Figure 183, which ro- 
tates freely between the permanent magnets. A clock- 
work geared to the upper end of the shaft records the 
revolutions of the armature. The scheme of connec- 
tion is plainly shown in Figure 184. 

The armature and the shunt field S are always in cir- 
cuit, but as their resistance is very high the current is 
small. The tendency to turn, due to the current in 
the armature, is only affected by the voltage across the 
mains. If the two field coils were replaced by perma- 
nent magnets we would have in reality an instrument 
which would, with a suitable arrangement of springs 
and a pointer, serve as a voltmeter and would only 
be affected by changes in voltage across the mains. 
The two coils M M, which are connected in series Avith 
one of the mains, form the field in which the armature 
rotates. The greater the strength of this field, the 
greater the speed of the armature. It will therefore 
be seen that the effort which revolves the armature 
is the result of the current in the coils M ]\I and the 
E.M.F. in the armature, the combination of these two 
being I X E or watts. 

In order that the speed of the armature may be in 
exact proportion to the Avatts used, a copper or alumi- 
num disk attached to the armature shaft is arranged 
to rotate, Avithout touching, between a pair of perma- 
nent magnets. A current is generated in this disk, in 
a manner similar to that in Avhich current is generated 
in the armature of a dynamo, and tends to retard the 
disk. The effect of this retardation is such that the 



Recording Wattmeters 313 

rate at which the armature revolves is in exact pro- 
portion to the wattage used on the circuit. 

Although every effort is made to reduce the friction 
to the smallest extent possible, by providing jewel 
bearings and by making the armature, shaft and disk 
of very little w^eight, still it is impossible to entirely 
do away with it. Some energy, although a very small 
amount, is also required to operate the clockwork of 
the registering mechanism. The shunt field S, con- 
nected in series with the armature circuit, is so ar- 
ranged that it tends to start the armature and over- 
come the friction of the revolving element. The meter 
will, therefore, register on light loads and register 
more accurately at all other loads. As the torque ex- 
erted by the shunt field is the result of the current in 
it and that in the armature, it is evident that a change 
in the voltage across the mains will also affect the start- 
ing torque, the variation being proportional to the 
square of the E.M.F. The shunt field should therefore 
be adjusted for the voltage of the circuit on which it 
is to be used. 

It will be noted that the connection for the shunt 
field is made on the load side L of the meter. With 
this connection the meter will register the amount of 
current used in the armature circuit. On the other 
hand, if the connection for the shunt field circuit was 
made on the generator side of the meter it would 
receive a slightly higher pressure and take into ac- 
count the loss in the main coils M M. The loss in 
either case is very small. 

Meters of the Thompson type may be used with 
either direct or alternating current circuits as there 



314 Operating and Testing 

is no iron used in their construction and the inductance 
is therefore small. Where used on alternating current 
circuits the reversals of the current in both the arma- 
ture and fields occur at the same time and the meter will 
continue to revolve in the one direction, for, it is well 
known, changing the direction of current in a shunt 
motor does not change the direction of rotation of the 
armature. If, however, the meter is fed from the 
wrong side it will run backward. This can readily be 
understood by referring to Figure 184. As long as 
the polarity of the supply circuit is not reversed the 
armature current remains in the same direction but 
the direction of the current through the fields depends 
upon from which side the meter is fed. 

For the measurement of power on alternating cur- 
rent circuits meters of the induction type possess a 
number of advantages and are used almost exclusively. 
These meters are used on alternating current circuits 
only, the rotation of the revolving element being ob- 
tained by the joint action of a set of series coils and 
a shunt coil inducing current in a metal disk. The 
reaction of this induced current causes the armature 
to revolve in much the same way as that of an ordi- 
nary induction motor. As the same disk is acted upon 
by both the coils which produce the rotation and the 
permanent magnet which retards the rotation the 
weight and consequently the friction may be kept 
dowTi to a minimum. The use of a commutator and 
its brushes are unnecessary as there is no winding on 
the revolving element. 

Figure 185 shows a view of the Guttman wattmeter 
with the dials and magnets removed. The aluminum 



Recording Wattmeters 



315 



armature which is slotted in spiral lines weighs about 
% of an ounce and rests on a jewel bearing. At the 
top of the spindle is a worm whereby the motion of the 
revolving element is transmitted to the recording 
train. The two series coils, shown directly at the left 
of the spindle, are mounted on aluminum frames. The 




Figure 185 

coils are wound with heavy wire and consume from 
two to four watts, depending on the size of the meter. 
The shunt coil of the meter is wormd upon a lami- 
nated iron core having two air gaps, through one of 
which the disk rotates. On the lower part of this 
laminated core a heavy band of copper partially sur- 
rounds the iron laminations. An adjustable piece of 



316 Operating and Testing 

wire is connected to the two ends of the copper band 
and completes an electrical circuit. 

In order that the meter may register accurately on 
inductive loads it is necessary that the current in the 
shunt field lag behind that of the series field by an 
angle of 90^^. This will be clearly understood by con- 
sidering the conditions which would exist were the 
two currents in exact phase. If such was the case 
the instrument would become a recording volt-ampere 
meter and would take into account only the amperes as 
they would be indicated by an ammeter. On an induc- 
tive load the product of the volts and amperes does not 
represent the wattage and to obtain the true value of 
the watts the power factor must be considered. 

The greatest torque or turning moment must be ex- 
erted on the revolving element of the meter when the 
load is non-inductive, for then the power factor is 1 
and the product of the volts and amperes represents 
the true power. On the other hand the least torque 
should be in effect when the load is all inductive or 
when the power factor is 0, for then there is no true 
energy represented. 

In order that the current in the shunt coil may lag 
90° behind the impressed E.M.F. this coil is wound 
on the iron core to give this circuit the greatest pos- 
sible inductance, but as this inductance alone cannot 
produce a difference of phase of 90° other means must 
be resorted to. This is accomplished by means of the 
copper band referred to above, which, forming a closed 
circuit around this iron core, has a current induced 
in it, and this current reacting upon the field pro- 
duced by the shunt coil gives the effect desired. 



Recording Wattmeters 



317 



INSTALLATION OF METERS 

The manner in which a meter is connected into the 
circuit depends upon the wiring system, and the cur- 
rent and voltage used. Although the structural feat- 
ures of the yarious makes of meters differ the general 
scheme of connecting them into the circuit is similar. 
■ Figure 184 shows the Thompson meter as used on a 
two-wire circuit. Both mains are carried to the meter, 
one of them being connected to the series coil and the 



a — ' 



T 



'Mj b-^^ 



IWVWWW 



T 



Figure 186 

other passing through the meter by the bus bar con- 
nection. The shunt armature circuit is, how^ever, con- 
nected to this bar. 

With large mains only one wire is carried through 
the meter, this being connected to the series coils. A 
tap taken off the other main connects to the shunt coil 
as shown in Figure 186. As this shunt tap carries, 
only current for the shunt field of the meter it may be; 
of small wire, generally No. 14 B. & S. gauge. 

When a meter is connected in a three-wire circuit 



318 



Operating and Testing 



both outside mains are carried through the meter, one 
through each of the series coils. The shunt field is 
connected by means of a wire tap to the neutral main. 
The Thompson three-wire meter is shown in Figure 
187. In some types of three-wire meters no neutral 
tap is used, the shunt circuit being connected directly 
across the outside mains. This connection has an ad- 
vantage in that it does away with the running of one 
wire to the meter and, as the shunt field connection is 




Figure 187 



Figure 188 



inaccessible the possibility of tampering with the meter 
is reduced. It has, however, the disadvantage in that 
an added resistance must be placed in series with the 
shunt field when used on direct current circuits with 
the consequent increase in the power consumed by the 
meter. 

Figure 188 shows the connections for a meter on a 
balanced three phase circuit. One main is carried 
through the series coil of the meter and two taps from 
the other two main wires are carried to a common con- 



Recording Wattmeters 



319 



nection through an inductive resistance and connect 
to the shunt field circuit. 

On alternating current circuits of large capacity it 
is not advisable, for several reasons, to carry the 




Figure 189 

mains through the meter. A small current trans- 
former is connected in series with one of the mains, 
the secondary of the transformer being connected to 




Figure 190 

the meter as shown in Figures 189 and 190. If the me- 
ter is used on a primary circuit or on any circuit where 
the voltage is high a small potential transformer may 
be connected across the mains and the shunt field con 



320 



Operating ana Testing 



nected directly to the secondary as shown in Figures 
191 and 192. Various other combinations of both cur- 
rent and potential transformers are made use of; as, 
for instance, on a three-wire circuit of large capacity. 
In this case two current transformers are used, one on 
each main, the secondaries being connected to the 
series coils of the meter. 

Detailed instructions are generally sent out for the 
installation of individual meters but there are a few 




Figure 191 

general directions which apply to all. A meter is a 
somewhat delicate instrument and, although built to 
withstand ordinary usage, efficient operation demands 
careful and intelligent handling. As has been stated, 
the revolving element of recording wattmeters rests 
on jewel bearings. A slight jar is often all that is 
necessary to injure or break the jewel. For this rea- 
son 3C7ne means is always provided to remove the re- 
volving element from contact with the jewel when the 



Recording Wattmeters 



321 



meter is to be carried about or during transportation, 
and the moving element should never be placed in con- 
tact with the jewel until the meter is ready to be 
started. 

When a meter is unpacked it should be carefully 
cleaned and examined. Some care should be exer- 
cised in the choice of location for setting the meter. To 
obtain the most efficient operation it should not be 
placed where it will be subject to any vibration, neither 
should it be placed in an extremely hot or cold place 
or where subject to great extremes of temperature. 




Figure 192 



Locations where dust, moisture, or inflammable or cor- 
rosive vapors are present should also be avoided. 

The meter should be installed in a readily accessi- 
ble location and should be fastened to a solid up- 
right support. A hole for a supporting screw is gen- 
erally provided at the top of the meter and a screw 
(never use a nail) should be inserted at this point 
■first. The meter should then be leveled. A small 
spirit level may be used for this purpose or, where the 
meter has a disk, a small weight of some non-magnetic 
substance such as brass may be placed near the outer 



322 Operating and Testing 

edge of the disk. If the meter is not level the weight 
and disk will revolve to the lowest point. 

Place the weight on the front or back upper surface 
of the disk. If the disk rotates to the right or left that 
part of the meter toward which it rotates is low and 
the bottom of the meter should be moved in that di- 
rection. When the meter is level from right to left 
the disk and weight will not move when the weight is 
placed at the center of the disk at the front or back. 

Now place the weight on either side of the disk and 
note if the disk rotates to the front or back. If to the 
rear the back part of the meter is too low and the 
meter should be moved out at the top. If the disk ro- 
tates to the front that part of the meter is too low and 
should be moved out at the bottom. AYhen a perfectly 
level position has been obtained the weight will not 
move if placed on any part of the disk It is well to 
check back after the last leveling as the first position 
may have been altered. All the screws should now be 
set up. 

The wires may now be connected to the meter, be- 
ing careful to follow the wiring scheme applying to 
the particular meter. The wires should be thoroughly 
cleaned and the binding posts tightly set up to avoid 
any heating at these points. Now place the revolv- 
ing element on its jewel if this has not already been 
done and turn on the current and note if the meter 
revolves in the proper direction. The meter case may 
now be placed on the frame, paying special attention 
to see that the case closely fits into place and no open^ 
ing is left at the edges. 



Recording Wattmeters 323 

TESTING 

A recording wattmeter is so designed that with a 
given wattage passing through the meter a definite 
number of revolutions of the armature will result. 
For instance, on a certain type of meter it takes 18 
seconds to complete one revolution of the armature 
on 100 watts, or 1800 seconds for one revolution on 1 
watt. This is the equivalent of 1/1800 of one revolu- 
tion for one seond on one watt. On this type of meter 
the armature would require 1800 seconds to make one 
revolution while only one watt is passing through the 
meter and this is taken as the testing constant of the 
meter. To determine the wattage at any load multi- 
revolutions 

ply the revolutions per second, or , by the 

seconds 

constant. As an example: Suppose the meter made 

1 
one revolution in one second, — X 1800 =: 1800 watts 

1 

passing through the meter. 

In order that the same type of meter may be used 
on circuits of different voltages it is customary to in- 
troduce a resistance in series with the shunt circuit; 
so that no matter what voltage may be used on the 
meter the armature circuit will always have impressed 
upon it the same voltage. The number of revolutions 
of the armature will then be the same even though the 
voltage on the meter and correspondingly the wattage, 
has been increased. To make this meter indicate cor- 



324 OperaMng and Testmg 

rectly the train gear is altered to indicate correct 
readings. For instance, with a certain meter designed 
for use on a 110 volt circuit it requires 2000 revolutions 
of the armature to register 1000 watts. If the same 
meter was used on a 220 volt circuit, with a resistance 
in series with the shunt circuit so that the shunt cir- 
cuit would only receive 110 volts, the true wattage 
would be registered by arranging the gearing so that 
one revolution of the armature would produce twice 
the movement of the pointer on the dial. The testing 
constant would also be doubled. 

As meters of large capacity require a larger wire 
for the winding of the series coils, and as it is not ad- 
visable to run the meter at too high a speed, the field 
due to the series winding is cut down and fewer rev- 
olutions of the armature will result with a given load. 
In this case the train ratio and the testing constant 
are increased. 

Below are given the testing formulas for calibrating 
recording wattmeters. 

FORT WAYNE 

Rev. X 100 X Constant 
= Watts 



Seconds 
See Instruction Book for Constants. 

WESTINGHOUSE 

Eev. X Constant 



Watts 



Seconds 



Recording Wattmeters 325 

Constant = 1.2 X (Amp. X Volts as marked on 
dial). 

On types B and C, Constant = 2.4 X Amp. X Volts 
as marked on dial) . 

GENERAL ELECTRIC^ DUNCAN AND SCHEEFER 

Eev. X 3600 X Constant 

= Watts 

Seconds 

G. E. Non-Direct Reading, Constant on dial. 

G. E. Direct Reading, Constant found on disk. 

Duncan, Constant on dial. (Fort Wayne Induc- 
tion type.) 

Duncan, Constant on disk (Direct current and S. & 
H. Induction type). 

Scheefer Non-Direct Reading, Constant on dial. 



STANLEY 

Rev. X 100 X Constant 
Seconds 



= Watts 



Constant = Seconds required for meter to make 
revolution on 100 watts. 

Constant stamped on case. 

GUTTMAN 

Rev. X Constant 
■ = Watts 



Seconds 



326 Operating and Testing 

3600 
Constant = 



Train ratio as found on meter 



SANGAMO 

Rev. X Constant 
= Watts 

Seconds 

Constant found on back of meter. 
Any of these formulas may be rearranged for con- 
venience in testing. 

Revolutions X Constant 
( 1 ) Watts = 



(2) Revolutions = 



Seconds 
Watts X Seconds 



(3) Seconds = 



(4) Constant 



Error := 



Constant 
Revolutions X Constant 

Watts 
Watts X Seconds 

Revolutions 
Observed sees.— Sees. 



Sees. 



The testing of a wattmeter can be accomplished in 
several ways, the choice of method depending on the 



'Recording Wattmeters 



327 



accuracy desired and the apparatus at hand. One of 
the simplest methods is that of turning on a number of 
16 candlepower lamps and then counting the number 
of revolutions of the meter disk in a given time. The 
load is estimated and the meter checked up by using 
the formula of the type of meter under test. As an 
example : Suppose ten 16 candlepower lamps, taking 50 
watts each, are turned on. The time required for 
one revolution according to formula (3) would be 

1 X 1800 

Seconds = = 3.6 seconds. If the meter made 

500 




Figure 193 

exactly ten revolutions in 36 seconds it would be reg- 
istering correctly. At best this method is only ap- 
proximate as the wattage of the lamps must be esti- 
mated and this will vary considerably with different 
makes of lamps and lamps of different ages. 

To make this test more accurate a number of lamps 
may be prepared by ascertaining the watts consumed 
by each at several different voltages such as will be 
met with on the tests. These voltages and the corre- 
sponding wattages should be marked on labels on the 
lamps. When a meter test is made a reading should 



328 



Operating and Testing 



be taken of the voltage with a portable voltmeter and 
the exact load can then be determined. See Figure 
193. 

A regular service meter accurately calibrated in the 
shop or laboratory may be used in checking up other 
meters by connecting it in circuit as shown in Figure 
194. With the connection shown the voltage impressed 
on the shunt coils of the two meters is equalized and 
the inaccuracy which would result were the meters 
connected side by side, where the shunt coil of one 
meter would be subjected to the reduced voltage caused 



i 




Figure 194 ^ 

by the drop in the series field of the other meter, is 
avoided. If the two meters are of the same type and 
capacity the two revolving elements will rotate in uni- 
son when the meter being tested is correct. If the 
meters are of different capacity this must be taken 
into account. 

The most accurate test and the one more generally 
used is shown in Figure 195. Figure 195 shows cor- 
rections for a standard wattmeter. The wattmeter is 
sometimes replaced by a voltmeter and ammeter. On 
direct current circuits either method may be used, but 
the wattmeter is more convenient and accurate. For 



Recording Wattmeters 



329 



alternating currents the reading obtained by multiply- 
ing together the amperes and volts does not represent 
the true wattage of the circuit unless the load is non- 
inductive. For inductive loads a wattmeter must be 
used, but it is well to take both the wattmeter and the 
volt-ampere readings so that the power-factor may be 
known. 

Figure 196 shows connections for testing a three wire 
meter using one standard wattmeter. The load must 
first be balanced and the neutral fuse then opened. 




Figure 195 



This method is objectionable where the shunt coil of 
the meter under test is connected directly across the 
mains as the shunt coil of the standard wattmeter is 
subject to the variation in voltage between the neutral 
and the outside wires. To overcome this objection a 
multiplier may be used in series with the shunt coil 
of the standard meter and connection can then be made 
directly across the outside mains. If the shunt cir- 
cuit of the meter under test is connected between one 
of the outside mains and the neutral wire a test may be 
made by using one standard wattmeter and connecting 



330 



Operating and Testing 



up only one series coil of the meter under test at a 
time, or both series coils may be connected in series. 

The most accurate method of testing three-wire 
meters is by use of two standard wattmeters con- 




Figure 196 

nected as shoMn in Figure 197. The sum of the stand- 
ard meter readings should equal the reading of the 
meter being tested. In this case it is not necessary to 
balance the load. 




Figure 197 

It is of great importance for accurate testing that a 
good stop watch be employed, although for approxi- 
mate tests the second hand of the ordinary watch serves 
the purpose quite well. The longer the time of the 
test, using the latter method, the less the error. 



Becording Wattmeters 331 

When the apparatus is set up ready for the test, 
a small load, about 10 per cent of the full load capac- 
ity of the meter, is turned on. The number of revolu- 
tions made by the revolving element and the time over 
which the count is made are noted. By means of for- 
mula 1 the watts as indicated by the meter under 
test are compared with the wattage of the standard 
meter. The per cent of standard watts will be 

Meter watts X 100 

. Example: Suppose the revolv- 

Standard watts 

ing element made 13 revolutions in 90 seconds, the 
testing constant of the meter being 1800. AYatts = 

13 X 1800 

^ 260 watts. If the standard meter indi- 

90 

cated 250 watts the percentage of standard watts 

260 X 100 

would be = 104 per cent, or 4 per cent 

250 
fast. 

A method frequently used, and one by which the 
percentage error may be taken direct from a previ- 
ously prepared table, is as follows : Ascertain the watts 
of the connected load from the reading of the standard 
wattmeter. From the following formula determine 
the number of revolutions the meter under test should 

Watts of load X 60 

make in one minute. = 

Testing constant of meter 



332 Operating and Testing 

Eevolutions per minute. Now note the number of sec- 
onds required by the meter under test to complete this 
number of revolutions. If the number of revolutions 
are completed in exactly 60 seconds, the meter is cor- 
rect ; if not, the meter is fast or slow. Example : On a 
load of 150 watts it is found that exactly 5 revolutions 
are completed in one minute or 60 seconds. Testing 

constant of meter is 1800. According to formula 2 

I 
150 X 60 ! 

Revolutions = = 5. If this meter had com- 

1800 

60 X 100 

pleted 5 revolutions in 55 seconds it would be — 

^ 55 ! 

= 109.09 per cent, or 9.09 per cent fast. If five rev- ; 
olutions had been completed in 67.8 seconds, it would j 

60 X 100 \ 

be =z 88.5 per cent, or 11.5 per cent slow. \ 

67.8 ; 

The following table gives the per cent of error for 1 
time in fifths of a second. 2 



Becording Wattmeters 



333 





PER CENT ERROR 


TABLE FOR FIFTHS OF A 


SECOND 


• 


Time in 


Per Cent 


Time in 


Per Cent 


Time in 


Per Cent 


Time in 


Per Cent 


Seconds 


Fast 


Seconds 


Fast 


Seconds 


Slow 


Seconds 


Slow 


40.20 


49.25 


50.20 


19.52 


60.20 


0.33 


70.20 


14.52 


.40 


48.51 


.40 


19.05 


.40 


0.67 


.40 


I 14.77 


.60 


47.78 


.60 


18.58 


.60 


0.99 


.60 


15.01 


.80 


47.06 


.80 


18.11 


.80 


1.31 


.80 


1 15.25 


41.00 


46.34 


51.00 


17.65 


61.00 


1.63 


71.00 


15.50 


.20 


45.63 


.20 


17.19 


.20 


1.96 


.20 


1 15.73 


.40 


44.93 


.40 


16.73 


.40 


2.27 


.40 


15.96 


.60 


44.23 


.60 


16.28 


.6i) 


2.59 


.60 


1 16.20 


.80 


43.54 


.80 


15.83 


.80 


2.91 


.80 


16.43 


42.00 


42.86 


52.00 


15.38 


62.00 


3.22 


72.00 


1 16.66 


.20 


42.18 


.20 


14.94 


.20 


3.53 


.20 


1 16.89 


.40 


41.51 


.40 


14.50 


.40 


3.84 


.40 


1 17.12 


.60 


40.85 


.60 


14.07 


.60 


4.15 


.60 


1 17.35 


.80 


40.19 


.80 


13.64 


.80 


4.45 


.80 


1 17.58 


43.00 


39.53 


53.00 


13.21 


63.00 


4.76 


73.00 


1 17.81 


.20 


38.89 


.20 


12.78 


.20 


5.06 


.20 


1 18.03 


.40 


38.25 


.40 


12.36 


.40 


5.36 


.40 


1 18.25 


.60 


37.61 


.60 


11.94 


.60 


5.66 


.60 


1 18.47 


.80 


36.98 


.80 


11.52 


.80 


5.95 


.80 


1 18.70 


44.00 


36.36 


54.00 


11.11 


64.00 


6.25 


74.00 


1 18.92 


.20 


35.75 


.20 


10.70 


.20 


6.54 


.20 


I 19.14 


.40 


35.14 


.40 


10.29 


.40 


6.83 


.40 


1 19.35 


.60 


34.53 


.60 


9.89 


.60 


7.12 


.60 


1 19.57 


.80 


33.93 


.80 


9.49 


.80 


7.40 


.80 


1 19.79 


45.00 


33.33 


55.00 


9.09 


65.00 


7.69 


75.00 


1 20.00 


.20 


32.74 


.20 


8.69 


.20 


7.97 


.20 


1 20.21 


.40 


32.16 


.40 


8.30 


.40 


8.25 


.40 


1 20.42 


.60 


31.58 


.60 


7.91 


.60 


8.53 


.60 


1 20.63 


.80 


31.00 


.80 


7.53 


.80 


8.81 


.80 


1 20.84 


46.00 


30.43 


56.00 


7.14 


66.00 


9.09 


76.00 


1 21.05 


.20 


'29.87 


.20 


6.76 


.20 


9.36 


.20 


1 21.26 


.40 


29.31 


.40 


6.38 


.40 


9.63 


1 .40 


1 21.47 


.60 


28.76 


.60 


6.01 


.60 


9.90 


.60 


1 21.68 


.80 


28.21 


.80 


5.63 


.80 


10.17 


.80 


1 21.88 


47.00 


27.66 


57.00 


5.26 


67.00 


10.44 


77.00 


22.08 


.20 


27.12 


.20 


4.89 


.20 


10.71 


.20 


22.28 


.40 


26.58 


.40 


4.53 


.40 


10.97 


.40 


1 22.38 


.60 


26.05 


.60 


4.17 


.60 


11.24 


.60 


1 22.68 


.80 


25.52 


.80 


3.81 


.80 


11.50 


.80 


1 22.88 


48.00 


25.00 


58.00 


3.45 


68.00 


11.76 


78.00 


1 23.08 


.20 


24.40 


.20 


3.09 


.20 • 


12.02 


.20 


1 23.28 


.40 


23.96 


.40 


2.74 


.40 


12.28 


.40 


1 23.47 


.60 


23.45 


.60 


2.39 


.60 


12.53 


.60 


1 23.66 


.80 


23.15 


.80 


2.04 


.80 


12.79 


.80 


1 23.86 


49.00 


22.45 


59.00 


1.69 


69.00 


13.04 


79.00 


1 24.05 


.20 


21.95 


.20 


1.35 


.20 


13.29 


.20 


1 24.24 


.40 


21.46 


.40 


1.01 


.40 


13.54 


.40 


24.43 


.60 I 


20.97 


.60 


0.67 


.60 


13.79 


.60 


24.63 


.80 


20.48 


1 .80 


I 0.33 


.80 


14.04 


.80 


1 24.82 


50.00 


20.00 


60.00 


0.00 


70.00 


14.28 


80.00 


1 25.00 



The per cent of full load on which tests should be 
made will vary with the class of work on which the 
meter is used. Where the load connected to the meter 
is such that it will be used uniformly over the range of 



334 Operating and Testing 

the meter tests should be made at 10 per cent, 20 per 
cent, 30 per cent, etc., (10 per cent intervals) over the 
full range of the meter. On the other hand, if the load 
is such that only the full load connected to the meter 
is used, such as on an electric sign, more tests should 
be made at the full load capacity. On the ordinary 
residence load a test at 4 per cent and 100 per cent of 
full load will generally suffice. 

Meters carrying large loads should be tested every 
30 days. If the meter is placed where there is much 
jarring it Avill tend to run fast. 

All meters have a tendency to gain in speed because 
of the gradual weakening of the controlling magnets. 

Commutator troubles are tlie greatest source of in- 
accuracies of meters. Some operators insert small 
fuses in armature circuit. This is especially useful 
when there is danger from lightning. 

READING OF METERS 

As has been previously stated, the basis of all re- 
cording wattmeter readings is the kilo-watt hour, the 
equivalent of one kilowatt used for one hour. It is 
not necessary that exactly a kilowatt of current be 
used, or that the current be used for the exact period 
of one hour, but that the product of the watts and the 
hours shall equal 1000 watt-hours. For instance : A 
16 candlepower lamp taking 50 watts and burning for 
20 hours represents one kilo-watt hour. Twenty of 
these 50 watt lamps burning for a period of one hour 
also represent one kilo- watt hour. 

Meter readings are indicated by the positions of 
pointers which move over a number of dials as shown 



Becording Wattmeters 335 

in Figure 198, the difference between any two readings 
representing the amount of power used during the 
interval between these readings. The pointers shown 
on the dials in Figure 198 are so connected by means 
of clockwork that a total revolution of any pointer 
represents 1/lOth of a revolution of the pointer to 
the left of it. It will also be noted that each dial 
reads in opposite directions to the one next to it. 

At the top of the individual dials the value of the 
reading of that dial is shown. Where the figures given 
are followed by the letter ^^s" it signifies that each 
division of the dial represents the amount of current 
indicated by the figure at the top. For instance, in 
Figure 200 each division of the dial at the right rep- 
resents 1/lOth of one kilowatt and a total revolution 
of the dial 10/lOths or 1 kilowatt. In a like manner, 
each division of the second dial from the right repre- 
sents 1 kilowatt and a total revolution of the pointer 
on this dial, 10 kilowatts. 

If the figure given at the top of the dial is not fol- 
lowed b^^ the letter ^^s", or as shown in Figure 199, 
each division of the dial represents 1/lOth of the 
amount shown at the top of the dial, the dial at the 
right of Figure 199 indicating 9/lOths of 10 kilowatts 
or 9 kilowatts. 

The reading of a meter should always be from rig.ht 
(lowest dial) to left, each reading of the dial at the 
left being used as a check on the reading of the dial 
at the left. The following examples will make clear 
the manner of reading meters: 

In Figure 198 the right hand pointer registers 
9/lOths of 1000 watt hours or 900 watt hours; the 



336 



Operating and Testing 



pointer next to it registers 8 (it cannot have passed 
the figure 9 as the pointer on the dial at the left of it 
has not made a complete revolution) ; the middle dial 



1,000,000 



100,000 



10,000 




10.000.000 



1,000 



Figure 198 

also registers 8 ; as the middle pointer has not passed 
the 0, the 4th dial must be read 1 ; the last dial also 



10,000 



1,000 



100 




KILOWATT HOURS 



Figure 199 

indicates 1, making the total reading 1,188,900 watt 
hours. 

In Figure 199 the readings on the meter dial are 



Recording Wattmeters 



337 



shown in kilowatt hours. The first pointer at the right 
reads 9 ; as this pointer has not passed the mark, the 
dial to the left must be read 8 ; each of the remaining 




Figure 200 

dials also reads 8, the total reading being 8889 kilowatt 
hours^ 

In Figure 200 the readings are also given in kilo- 
watt hours. The pointer on the first dial at the right 




Figure 201 
has not passed the mark so this dial must be read 
9/lOths of a kilowatt hour or .9 ; the second dial reads 
5 ; the middle dial 6 ; the fourth dial 9 and the last 
dial 1, making the total reading 1965.9 kilowatt hours. 
In Figure 201 the dial at the right indicates 9 kilo- 



338 



Operating and Testing 



watt hours; the second dial 9; the third 4. and the 
fourth 9, making a total reading of 9499 kilowatt 
hours. 

On some types of meters a multiplier is used. This 
is generally given on the meter dial and the readings 
as indicated by the pointers should be multiplied by 
this number to obtain the correct reading of the meter. 

DISCOUNT METER 

Figure 202 shows a diagram of what is known as the 
Wright discount or demand meter. This meter is 




Figure 202 

used on circuits where it is desired to know the maxi- 
mum current which has passed through the circuit. 
In the diagram, B is a glass bulb connected to a tube 
U which is partly filled with a liquid. Around bulb 
B is wound a resistance wire which carries the main 
current. When current flows in this wire heat is 
generated and the air in the bulb is expanded, thus 
forcing the liquid around tube U until it reaches the 
point where tube U and I join, when it will flow into 



Recording Wattmeters 



33y 



Maximum 

Current In 

Amperes 



10 



Kilowatt hrt. 
at Full Rate 



30 



25 



20 



SizelOAmp 
No. 42466. 



15 



10 



Mtiltiply 
\>y 2 on 
230.. volt 
circuits 



•CALK OF DISCOUNT METER 



Figure 203 

tube I. The amount of liquid in tube I will depend 
upon the maximum current which has passed through 
the resistance wire on bulb B. The meter is not af- 



340 Operating and Testing 

fected by momentary increases in current. If the 
maximum current lasts five minutes, 80 per cent will 
register ; ten minutes, 95 per cent will register ; thirty 
minutes, 100 per cent will register. Figure 203 shows 
the scale of this- meter. The left-hand scale shows the 
maximum current used in amperes and the right-hand 
scale the kilowatt hours for which the customer must 
pay full rate. 

As, a discount meter, this meter is connected in se- 
ries with one of the mains connecting to the ordinary 
recording wattmeter. On three-wire circuits a dis- 
count meter must be connected in each main, this re- 
quiring two meters. As the scale is computed for 115 
volt circuits, when the meter is used on a 230 volt cir- 
cuit the reading must be doubled, as indicated at the 
bottom of the scale. 

The recording wattmeter registers the total con- 
sumption of energy and the discount meter the pro- 
portion of it to be charged at full rate. The excess 
of the recording wattmeter reading over the discount 
meter reading is subject to the lower rates as specified 
by the lighting company. In case the wattmeter read- 
ing is less than the discount meter reading only the 
consumption as shown by the recording wattmeter is 
charged at the full rate. 

The discount meter shows the full rate portion of 
the bill for one month of 30 days. When computing a 
bill for a greater or less time the reading should be 
proportioned according to the time. After each 
monthly reading the meter is opened and the tube 
tipped up until all the liquid flows out. If there is 
current in the meter, the liquid will flow back again 



Recording Wattmeters 341 

when the tube is turned down ; otherwise the tube will 
remain empty until current is used. 

The purpose for which this discount meter is used 
is to obtain a more equitable basis for the charge for 
current. As practically all users of current, for light- 
ing for instance, use the maximum amount of current 
at the same time, the cost to the lighting companies of 
both the generation of this current and transmission of 
it to the consumer is a maximum at this time. They 
must have sufficient generating apparatus and trans- 
mission lines to supply the demand and the line losses 
at this time are considerably greater. This extra 
equipment must be maintained for the short interval 
during which this extra demand is made, or at the 
peak of the load. 

It is assumed that a consumer will use the maximum 
amount of current for one hour each day during the 
thirty days of the month, and the kilowatt hours to be 
paid for at full rate are computed on this basis. Sup- 
pose a current of ten amperes was indicated by the 
maximum meter as the greatest amount of current 
used during the month. Ten amperes at 115 volts 
amounts to 1150 watts, and this amount used for 
one hour a day for 30 days represents 30 X 1150 
= 34,500 watt-hours or 34.5 kilowatt-hours as the 
amount of current to be paid for at the full rate. 
An examination of the meter scale as shown in Figure 
22 will show that a current of ten amperes is equiva- 
lent to 34.5 kilowatt-hours at the full rate. 



CHAPTER XXII 

LIFE AND FIRE HAZARD 

Electricity may endanger life or seriously maim in 
two ways : By direct contact, causing severe shock and 
often instant death, and by burning through the me- 
dium of a flash or arc which may also prove destruc- 
tive to the eyesight. 

A shock may be obtained by touching wires of oppo- 
site polarity; by touching one wire and making con- 
nection to the ground, the other wire being grounded, 
or by cutting one 's self into the circuit. 

It is perfectly safe to touch any one bare wire pro- 
vided one is perfectly insulated from the ground, and 
even if one is not insulated, if the wires are clear from 
the ground no harm will be done, but under no circum- 
stances should one ever trust a system of wiring, a 
ground may come on at any moment and cause instant 
death. The general rule for handling live wires of 
high potential is, to use only one hand at a time and 
keep well insulated from the ground and from wires of 
opposite polarity. 

While working on dead lines that are connected with 
stations over which the workman has no control and 
which may be connected up by mistake at any moment, 
it is a good plan to short circuit those wires and 
ground them. If now the station attendant should 

342 



Life and Fire Hazard 343 

throw in switches no harm would be done except to 
his fuses 

Whenever it is necessary to cut wires carrying cur- 
rent, they should be merely cut into a little with the 
pliers (to cut clear through will bum the pliers) and 
then the wire may be broken, but under no circum- 
stances should one bridge the cut with arms or hands. 
The breaking of the circuit will produce an enormous 
voltage for an instant which may be amply sufficient 
to cause death to any one holding the ends of a broken 
wire. If a high potential circuit is to be broken in 
this way it is best to work the wire in two with a stick. 

The severity of a shock obtained from a circuit will 
depend upon the voltage of the circuit, the degree of 
contact the person makes with the wires, the condition 
of the body where it touches, whether moist or dry, 
and the quality of the ground which may be helping to 
make the circuit through the body. Thus it is by no 
means always safe to touch a live wire of 200 volts nor 
always fatal to receive a shock from 2000 volts. 

Many people have been killed by the lower voltage 
and many have escaped unharmed from shocks ob- 
tained from the higher pressure. 

The greatest danger to the eyesight and from burns 
is encountered while fusing up or throwing in switches 
on circuits carrying heavy currents. Many switches 
are built so that the handle is directly above the fuses. 
In case such a switch is thrown in w^hile there is a 
short circuit on the line the operator 's hands are likely 
to be burned very badly. It is best to cover the fuses 
with asbestos or to procure a stick with which the 
switch may be pushed in. 



344 



Operating and Testing 



"Where circuits are controlled by circuit breakers 
there should always be a switch which must be open 
until the breaker is set so that the hand may not inter- 
fere if the breaker should start to go out at once be- 
cause of overload or short circuit. 

To install fuses in a live circuit which cannot be 
disconnected by switches is always a matter attended 
with some risk. As a rule the nature of the ^^blowV' 



ih 



D 




Figure 204 

will give some idea as to whether it was caused by an 
overload or a short circuit. The current due to a short 
circuit will generally be many times greater than that 
of an overload owing to the fact that it requires some 
time for the fuse to heat. If there is indication that 
there is a short circuit, tests had better be made before 
attempting to install the proper fuses. A circuit sup- 
plying a large number of lights cannot be tested for 



Life and Fire Hazard 345 

^^ short" in the ordinary manner because the lights 
establish a circuit of low resistance. If both fuses are 
out, the best way to test it is, by connecting a small 
fuse into the circuit, trying one side of the fuse block 
at a time. If there should happen to be two grounds, 
as at H and K, Figure 20-4, a fuse installed at 1 will 
not blow^, but placed in 2 it will. If each side singly 
holds a small fuse without blowing, a fuse of the 
proper size may be safely installed on one side. When 
this is done a piece of wire of suitable size may be 
fastened to one of the terminals on the opposite side 
and this wire used to bridge the other fuse gap The 
wire should be of such a length that the workman need 
not endanger his eyes or hands w^hile making connec- 
tion. If the fuses in question are very large the first 
fuse may be covered with asbestos. If the first fuse 
does not blow w^hen the circuit is completed with the 
wire (know^n as a *' jumper") the second may be in- 
stalled, leaving the wire to carry the current until 
the fuse is in place. 

The fire hazard of electric wiring consists in the 
possibility of overheating wires when carrying too 
much current; where circuits are broken an arc is 
always established which may communicate fire; 
where wires come in contact with wood moisture may 
cause a ground along which current may flow, event- 
ually ^^.harring the wood and starting a fire ; wires may 
come in contact with gas pipes and gradually, by mak- 
ing intermittent contact, eat holes into the pipe, al- 
lowing gas to escape which finally is fired by the 
spark. 

Lamps and motors may also become so much over- 



346 Operating and Testing 

heated as to communicate fire to combustible material. 
Many fires are also caused by small sparks as from 
switches and sockets setting fire to gases or lint in 
factories. 

An incandescent lamp ordinarily does not become 
very hot but when covered over with paper or cloth 
or when subject to an abnormal voltage it may easily 
cause fires. Many of them have done so. 



CHAPTER XXIII 

GROUND DETECTORS AND LIGHTNING ARRESTERS 

As a rule all systems of wiring should be kept free 
from grounds. The exceptions to this rule are three- 
wire systems of such magnitude that it becomes prac- 
tically impossible to do so, and in such cases the neutral 
wire is permanently grounded. 

In some cases it may be advisable to install ground 
detectors that give continuous indications, but as such 
indicators introduce a permanent ground which un- 
der favorable circumstances becomes an aid in break- 
ing down the insulation of the opposite polarity from 
the one to which it is attached, this is not generally de- 
sirable. 

Either of the lamp systems of ground detectors here 
described can be made continusuoly indicating by per- 
manently closing the switch which connects the lamps 
to ground and voltmeters may be used in place of the 
lamps. 

Figure 205 is the simplest and cheapest of all 
ground detectors. Only two lamps and a push button 
are required. As long as the lamps are not connected 
to the ground, they burn in series at about half can- 
dlepower. If the switch is kept closed and a ground 
occurs on one side of the system, the lamp on that side 

347 



348 



Operating and Testing 



burns dull and the other becomes brighter. If the 
ground is very- ''good/' the lamp on the side of the 
ground will be entirely extinguished and the other will 
be at full candlepower. 

Figure 206 shows method of using voltmeter as 



7 




Figure 205 Figure 206 

ground detector. The lamps shown above are not very 
sensitive and will not indicate a slight ground. Hence 
the voltmeter is preferable. As long as both buttons 
are in their normal position, the voltmeter measures 
the voltage of the system. By pressing dowa either 




Figure 207 

button, if a deflection is obtained, it indicates a ground 
on that side of the system to which the button belongs. 
Figure 207 shows ground detector connections using 
lamps for an ordinary three-wire or three-phase sys- 
tem. Used in connection with the ordinary three-wire 



Orotmd Detectors and Lightning Arresters 349 

\vstem, no indication will be obtained while the switch 
:s connected to the leg that is grounded. If one leg is 
grounded the lamps will be either at full or half can- 
dlepower, depending upon w^hich leg the switch is 
x>laced. 

AVith three-phase systems, also, no indication will be 
obtained as long as the sw^itch is connected to the 
grounded leg. AVhen it is connected to the other legs 
the lamps will burn bright. 

Another ground detector for three-phase systems is 
shown in Figure 208. 




Figure 208 



With this connection as long as the line is clear the 
two voltmeters show even pressure. With a ground 
coming on one side, say at X, voltmeter 1 will read 
lower and 2 higher ; with a ground on the opposite sidt 
2 will read low and 1 high. With a ground on the mid- 
dle wire, both will read higher. 

Ground detectors like the above are reliable only if 
one side of the system is clear. The ground on any 
side acts as a shunt to the lamp on that side and if such 
shunts exist on both sides, it is clear that the indica- 
tions will be confusing. Tests should, therefore, be 
frequently made so as to be reasonably sure that a 
ground will be detected as soon as it comes on. 



350 



Operating and Testing 



If a system is to have a thorough test, it must be 
disconnected and tested with a Wheatstone bridge or 
other method described elsewhere. 



LIGHTNING ARRESTERS 



A lightning discharge takes place only in obedience 
to an enormous pressure and is of very short duration. 
During this exceedingly short time the counter E.M.F. 
of magnets and other inductive arrangements is so 




Figure 209 

great that it is easier for the current to jump a small 
air gap than force its way over an ordinary transmis- 
sion line. 

The simplest form of lightning arrester is sho\\Ti in 
Figure 209. When the discharge occurs, the current 
jumps the spark gap between the two metal plates M. 
If these are connected to a dynamo circuit carrying 
much current, the arc established by the lightning dis- 
charge will be maintained by the dynamo and the re- 
sult will be a short circuit. This type of arrester can, 



Ground Detectors and Lightning Arresters 351 

therefore, be used only in connection with circuits such 
as telegraph or telephone in which the currents are not 
of sufficient strength to maintain an arc. 

A single plate of this kind is also useful if mounted 
closely to belts which give trouble from static charges. 

The best known type of lightning arrester is that 
of Prof. Thomson. In this, the arc which is established 
by the discharge, is immediately blown out magnetic- 
ally by the dynamo current. Entering at L, Figure 




; 



Figure 210 



Figure 211 



210, the lightning jumps the gap G and passes to 
ground. The magnetism existing in the coil forces 
the arc upward until it breaks It is essential that 
this arrester be so connected that the side L is toward 
the outside lines. 

Another form of lightning arrester is illustrated in 
Figure 211. This form is used with alternating cur- 
rent circuits only. It consists of three cylinders placed 
very close together as shown. These cylinders may be 
of non-arcing metal, and besides offer such a large sur- 



352 Operating and Testing 

.face over which the arc spreads that it does not create 
a high enough temperature to maintain itself. Ordi- 
narily only a very small spark is noticed. 

For use with high voltages either of the foregoing 
forms may be connected in series. Each wire leading 
overhead to the outside should be protected. The 
ground wire for lightning arresters should be as 
straight as possible ; should be of copper, never of iron 
and should not be run in proximity to iron. 



INDEX 

Page 

Acc^imulators 174 

Acme testing set 262 

Alternating current : 44-68 

Alternating current motors 86-148 

Alternating current motors, types of 96 

Alternators, operation of 124 

Ammeters 255 

Ampere 15 

Ampere turns 26-28 

Arc dynamo 60 

Arc dynamo, starting of 106 

Arc lamps 184 

Arc lamps on alternating current circuits 187 

Armature, heating of 301 

Auto-starter 149 

Balancing set 120 

Batteries, primary 170 

Battery rooms , 176 

Belts 102 

Booster 177 

Brush arc dynamo 60 

Brushes, shifting of 53 

Candlepower of arc 192 

Candlepower, test for 291 

Carbons for arc lamps 188 

Charging storage batteries 177 

Circuit testing 275 

Circular millage of wires 286 

Closed circuit batteries 172 

Compass needle 245 

Commutator 44 

Compensator 120 



Index 

Compound wound dynamo 65 

Compound wound dynamos in parallel 114 

Compound wound motors 84 

Condensers 11 

Conductivity of metals 12 

Cooper Hewitt lamps 240 

Coulomb 16 

Counter — electromotive of motors 76 

Cross currents 128 

Delta connected transformers 163 

Delta connected armature 100 

Differential arc lamp 200 

Differential wound motor 85 

Direction of flow of current 8 

Direction of flow of induced current 40 

Discount meter 338 

Distribution of light from incandescent lamps 235 

Drum armatures 47 

Dynamo-electric machines 39 

Dynamos, operation of direct current 102 

Dynamos, testing of 269 

Dynamo troubles 298 

Dynamos, types of : ^^ 

Efficiency of dynamos 270 

Efficiency of incandescent lamps 219 

Efficiency of motors 270 

Efficiency of transformers 167 

Equalizer wires 114 

Enclosed arc 193 

Electric current 7 

Electric induction 153 

Electrolysis, testing for 287 

Electrolyte for storage batteries 175 

Electromagnets, heating of 36 

Electromagnets, winding of 35 

Electro-magnetic induction 42 

Electromotive force 7 

Farad 16 



Index 

Field magnet 39 

Fixture testing 283 

Flaming arc 205 

Foucault currents 157 

Galvanometer, tangent 246 

Galvanometer, mirror 248 

Gramme ring armature 47 

Gravity cell 172 

Ground detector 347 

Grounding, dynamo frames 107 

Grounding, transformers 167 

Grounds, testing for .275-347 

Henry 18 

High potentials, handling of 168 

Hysterisis 33 

Illumination from arc lamps 194 

Hlumination from incandescent lamps 234 

Incandescent lamps 217 

Incandescent lamps, efficiency of, with variation in volt- 
age 223 

Induced currents 10 

Induction motors 90 

Installation of meters 317 

Instruments for testing 243 

Insulation resistance, testing for, with voltmeter 270 

Insulators 12 

Joule 17 

Kilowatt 308 

Laminating cores 33-157 

Leclanche batteries 173 

Life and fire hazard 342 

Life of incandescent lamps 224 

Lightning arresters 350 

Lines of force 21-24 

Loss, testing for 284 

Magnets 265 

Magnets, bar 20 

Magnets, electro 23 



Index 



Magnetic flux , . . . 25 

Magnetism 19 

Magnetomotive force = 25 

Maximum demand meter 338 

Mirror galvanometer 248 

Mercury arc lamp 240 

Mercury arc rectifier 180 

Mercury rectifier for arc lamps 215 

Mesh winding, armature 100 

Metallized filament lamp 230 

Meter, discount 338 

Meter, installing 317 

Meter reading 334 

Meter, testing of 323 

Meter, three-phase 318 

Meter, three-wire 318 

Motor troubles 302 

Motors, alternating current 148 

Motors, direct current 74 

Motors, operation of 145 

Motors, testing of 269 

Motors, three-phase 149 

Motors, types of, direct current 80 

Multiple arc . . 196 

Mutual induction 155 

Kernst lamps 239 

Neutral point 53 

No-voltage release 145 

Ohm : 14 

Open circuit battery 172 

Open circuit, test for 278 

Operation of arc lamps 207 

Overload release 145 

Parallel circuits 11 

Parallel operation of alternators 126 

Parallel operation of direct current dynamos 112 

Photometry 291 

Polarity, testing for dynamos 109-116 



Index 

Polarized magnet 32 

Power factor 133 

Primary battery 170 

Prony brake 273 

Racing of motors 304 

Range of carbons 188 

Rating of arc lamps 191 

Rating of incandescent lamps 221 

Reading of meters 334 

Recording wattmeters 307 

Rectifier, for alternating current dynamos 71-124 

Rectifier, for arc lamps , . 215 

Rectifier, mercury arc 180 

Regulator, series arc 214 

Resistance, magnetic 26 

Reversing alternating current motors 150 

Rheostat, field 51 

Rheostat, starting 145 

Ring armature 47 

Rotary converter, operation of 133 

Rotor 95 

Series arc 196 

Series arc switchboard 211 

Series circuit 11 

Series dynamo 56 

Series motor 80 

Series operation of arc machines 109 

Shunt dynamo : 63 

Shunt dynamos in parallel 112 

Shunt dynamos, starting of Ill 

Shunt for ammeter 256 

Shunt motor 83 

Slip of induction motor. 94 

Smashing point of incandescent lamps 225 

Solenoid 30 

Sparking of brushes 299-304 

Squirrel cage armature 94 

Star connected transformer 163 



Index 

Star winding, armature 100 

Starting box, automatic 145 

Stator 95 

Step-down transformer 152 

Step-up transformer 152 

Stillwell regulator 133 

Storage batteries 174 

Switchboard, charging storage batteries 178 

Switchboard, series arc 211 

Synchronizing alternators 126-130-134 

Synchronous motors 89 

Synchroscope, Lincoln 139 

Tangent galvanometer 246 

Tantalum lamp 231 

Telephone receiver for testing 266 

Testing, arc lamps 210 

Testing, carbons 188 

Testing, circuits 275 

Testing, connections on interior wiring 282 

Testing, dynamos and motors 269 

Testing, electrolysis 289 

Testing, fixtures 283 

Testing, incandescent circuits 279 

Testing, instruments for 243 

Testing, for loss 284 

Testing, meters 323 

Testing, polarity 129-281 

Testing, rail bonds 291 

Testing, transformers 165 

Thomson wattmeters 311 

Thomson-Houston dynamo 62 

Thomson-Houston arc switchboard 211 

Three-phase transformer connections 164 

Three-wire systems 184 

Three-wire transformers 161 

Transformers 151 

Transformer connections 159 

Transformers in parallel 163 



Index 

Trimming arc lamps 207 

Tungsten lamps 232 

Two-wire meters 311 

Volt 16 

Volt, production of 41 

Voltmeter 255 

Watt 308 

Watt-hour 309 

Wattmeter, recording 307 

Weston instruments 250 

Wheatstone bridge 257 



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PUBUSHERS OF SFXF-EDUCATIONAL BOOKS 
132S Michigan Avenue CHICAGO 



A BOOK EVERY ENGINEER AND ELECTRICIAN 
SHOULD HAVE IN HIS POCKET. A COMPLETE 
ELECTRICAL REFERENCE LIBRARY IN ITSELF 



^he Handy Vest-Pocket 

ELECTRICAL 
DICTIONARY 

By WM, L,. WEBER, M.E. 
ILLUSTRATED 

CONTAINS upwards of 4,800 words, 
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Cloth, Red Edges, Indexed . • 25c 
Full Leather, Gold Edges, Indexed, 50c 

Sold by •Dooksellers generally or sent postpaid to any address upon receipt 

of price. 

FREDERICK J. DRAKE & CO. 

PUBLISHERS 




CHICAGO. 



ILUNOIf 



THE AUTOMOBILE HAND-BOOK 

OVER 200,000 SOLD 
By ELLIOTT BROOKES, Atsissted by Other Well-Known Experts 

Revised and Enlarged New Edition— The largest and most practical 

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over 329 illustrations. Full Leather Limp, Round 

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FREDERICK J. DRAKE & CO., Publishers 

1325 Michigan Avenue. ' > > CHICAGO, U. S. A. 




The Practical Gas €? 
Oil Engine hand, boo k 




MlllONRRYMAmNE Ati« 
■limits ANDCASdM 




A MANUAL of useful in- 
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Pocket size, 4x6H. 
232 pages. With numerous 
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This book has been written 
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In treating the various subjects £t has been the endeavor to avoid all 

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|6mo. PopuIoLr Cdition—CIoth. Price $1.00 

Edition de Luxe— Full LeaLtKer Limp. Price ... 1.59 

Sent Postpaid to any Address in the World upon Receipt of Price 

FREDERICK J. DRAKE & CO. 

PUBLISHERS 



